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RFC 3744 - Web Distributed Authoring and Versioning (WebDAV) Acc


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Network Working Group                                           G. Clemm
Request for Comments: 3744                                           IBM
Category: Standards Track                                     J. Reschke
                                                              greenbytes
                                                               E. Sedlar
                                                      Oracle Corporation
                                                            J. Whitehead
                                                         U.C. Santa Cruz
                                                                May 2004

           Web Distributed Authoring and Versioning (WebDAV)
                        Access Control Protocol

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   This document specifies a set of methods, headers, message bodies,
   properties, and reports that define Access Control extensions to the
   WebDAV Distributed Authoring Protocol.  This protocol permits a
   client to read and modify access control lists that instruct a server
   whether to allow or deny operations upon a resource (such as
   HyperText Transfer Protocol (HTTP) method invocations) by a given
   principal.  A lightweight representation of principals as Web
   resources supports integration of a wide range of user management
   repositories.  Search operations allow discovery and manipulation of
   principals using human names.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
       1.1.  Terms. . . . . . . . . . . . . . . . . . . . . . . . . .  6
       1.2.  Notational Conventions . . . . . . . . . . . . . . . . .  8
   2.  Principals . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Privileges . . . . . . . . . . . . . . . . . . . . . . . . . .  8
       3.1.  DAV:read Privilege . . . . . . . . . . . . . . . . . . . 10
       3.2.  DAV:write Privilege. . . . . . . . . . . . . . . . . . . 10
       3.3.  DAV:write-properties Privilege . . . . . . . . . . . . . 10
       3.4.  DAV:write-content Privilege. . . . . . . . . . . . . . . 11
       3.5.  DAV:unlock Privilege . . . . . . . . . . . . . . . . . . 11
       3.6.  DAV:read-acl Privilege . . . . . . . . . . . . . . . . . 11
       3.7.  DAV:read-current-user-privilege-set Privilege. . . . . . 12
       3.8.  DAV:write-acl Privilege. . . . . . . . . . . . . . . . . 12
       3.9.  DAV:bind Privilege . . . . . . . . . . . . . . . . . . . 12
       3.10. DAV:unbind Privilege . . . . . . . . . . . . . . . . . . 12
       3.11. DAV:all Privilege. . . . . . . . . . . . . . . . . . . . 13
       3.12. Aggregation of Predefined Privileges . . . . . . . . . . 13
   4.  Principal Properties . . . . . . . . . . . . . . . . . . . . . 13
       4.1.  DAV:alternate-URI-set. . . . . . . . . . . . . . . . . . 14
       4.2.  DAV:principal-URL. . . . . . . . . . . . . . . . . . . . 14
       4.3.  DAV:group-member-set . . . . . . . . . . . . . . . . . . 14
       4.4.  DAV:group-membership . . . . . . . . . . . . . . . . . . 14
   5.  Access Control Properties. . . . . . . . . . . . . . . . . . . 15
       5.1.  DAV:owner. . . . . . . . . . . . . . . . . . . . . . . . 15
             5.1.1. Example: Retrieving DAV:owner . . . . . . . . . . 15
             5.1.2. Example: An Attempt to Set DAV:owner. . . . . . . 16
       5.2.  DAV:group. . . . . . . . . . . . . . . . . . . . . . . . 18
       5.3.  DAV:supported-privilege-set. . . . . . . . . . . . . . . 18
             5.3.1. Example: Retrieving a List of Privileges
                    Supported on a Resource . . . . . . . . . . . . . 19
       5.4.  DAV:current-user-privilege-set . . . . . . . . . . . . . 21
             5.4.1. Example: Retrieving the User's Current Set of
                    Assigned Privileges . . . . . . . . . . . . . . . 22
       5.5.  DAV:acl. . . . . . . . . . . . . . . . . . . . . . . . . 23
             5.5.1. ACE Principal . . . . . . . . . . . . . . . . . . 23
             5.5.2. ACE Grant and Deny. . . . . . . . . . . . . . . . 25
             5.5.3. ACE Protection. . . . . . . . . . . . . . . . . . 25
             5.5.4. ACE Inheritance . . . . . . . . . . . . . . . . . 25
             5.5.5. Example: Retrieving a Resource's Access Control
                    List. . . . . . . . . . . . . . . . . . . . . . . 25
       5.6.  DAV:acl-restrictions . . . . . . . . . . . . . . . . . . 27
             5.6.1. DAV:grant-only. . . . . . . . . . . . . . . . . . 27
             5.6.2. DAV:no-invert ACE Constraint. . . . . . . . . . . 28
             5.6.3. DAV:deny-before-grant . . . . . . . . . . . . . . 28
             5.6.4. Required Principals . . . . . . . . . . . . . . . 28
             5.6.5. Example: Retrieving DAV:acl-restrictions. . . . . 28

       5.7.  DAV:inherited-acl-set. . . . . . . . . . . . . . . . . . 29
       5.8.  DAV:principal-collection-set . . . . . . . . . . . . . . 30
             5.8.1. Example: Retrieving DAV:principal-collection-set. 30
       5.9.  Example: PROPFIND to retrieve access control properties. 32
   6.  ACL Evaluation . . . . . . . . . . . . . . . . . . . . . . . . 36
   7.  Access Control and existing methods. . . . . . . . . . . . . . 37
       7.1.  Any HTTP method. . . . . . . . . . . . . . . . . . . . . 37
             7.1.1. Error Handling. . . . . . . . . . . . . . . . . . 37
       7.2.  OPTIONS. . . . . . . . . . . . . . . . . . . . . . . . . 38
             7.2.1. Example - OPTIONS . . . . . . . . . . . . . . . . 39
       7.3.  MOVE . . . . . . . . . . . . . . . . . . . . . . . . . . 39
       7.4.  COPY . . . . . . . . . . . . . . . . . . . . . . . . . . 39
       7.5.  LOCK . . . . . . . . . . . . . . . . . . . . . . . . . . 39
   8.  Access Control Methods . . . . . . . . . . . . . . . . . . . . 40
       8.1.  ACL. . . . . . . . . . . . . . . . . . . . . . . . . . . 40
             8.1.1. ACL Preconditions . . . . . . . . . . . . . . . . 40
             8.1.2. Example: the ACL method . . . . . . . . . . . . . 42
             8.1.3. Example: ACL method failure due to protected
                    ACE conflict. . . . . . . . . . . . . . . . . . . 43
             8.1.4. Example: ACL method failure due to an
                    inherited ACE conflict. . . . . . . . . . . . . . 44
             8.1.5. Example: ACL method failure due to an attempt
                    to set grant and deny in a single ACE . . . . . . 45
   9.  Access Control Reports . . . . . . . . . . . . . . . . . . . . 46
       9.1.  REPORT Method. . . . . . . . . . . . . . . . . . . . . . 46
       9.2.  DAV:acl-principal-prop-set Report. . . . . . . . . . . . 47
             9.2.1. Example: DAV:acl-principal-prop-set Report. . . . 48
       9.3.  DAV:principal-match REPORT . . . . . . . . . . . . . . . 49
             9.3.1. Example: DAV:principal-match REPORT . . . . . . . 50
       9.4.  DAV:principal-property-search REPORT . . . . . . . . . . 51
             9.4.1. Matching. . . . . . . . . . . . . . . . . . . . . 53
             9.4.2. Example: successful DAV:principal-property-search
                    REPORT. . . . . . . . . . . . . . . . . . . . . . 54
       9.5.  DAV:principal-search-property-set REPORT . . . . . . . . 56
             9.5.1. Example: DAV:principal-search-property-set
                    REPORT. . . . . . . . . . . . . . . . . . . . . . 58
   10. XML Processing . . . . . . . . . . . . . . . . . . . . . . . . 59
   11. Internationalization Considerations. . . . . . . . . . . . . . 59
   12. Security Considerations. . . . . . . . . . . . . . . . . . . . 60
       12.1. Increased Risk of Compromised Users. . . . . . . . . . . 60
       12.2. Risks of the DAV:read-acl and
             DAV:current-user-privilege-set Privileges. . . . . . . . 60
       12.3. No Foreknowledge of Initial ACL. . . . . . . . . . . . . 61
   13. Authentication . . . . . . . . . . . . . . . . . . . . . . . . 61
   14. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 62
   15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 62

   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 62
       16.1. Normative References . . . . . . . . . . . . . . . . . . 62
       16.2. Informative References . . . . . . . . . . . . . . . . . 63
   Appendices
   A.  WebDAV XML Document Type Definition Addendum . . . . . . . . . 64
   B.  WebDAV Method Privilege Table (Normative). . . . . . . . . . . 67
   Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 71
   Full Copyright Statement. . . . . . . . . . . . .  . . . . . . . . 72

1.  Introduction

   The goal of the WebDAV access control extensions is to provide an
   interoperable mechanism for handling discretionary access control for
   content and metadata managed by WebDAV servers.  WebDAV access
   control can be implemented on content repositories with security as
   simple as that of a UNIX file system, as well as more sophisticated
   models.  The underlying principle of access control is that who you
   are determines what operations you can perform on a resource.  The
   "who you are" is defined by a "principal" identifier; users, client
   software, servers, and groups of the previous have principal
   identifiers.  The "operations you can perform" are determined by a
   single "access control list" (ACL) associated with a resource.  An
   ACL contains a set of "access control entries" (ACEs), where each ACE
   specifies a principal and a set of privileges that are either granted
   or denied to that principal.  When a principal submits an operation
   (such as an HTTP or WebDAV method) to a resource for execution, the
   server evaluates the ACEs in the ACL to determine if the principal
   has permission for that operation.

   Since every ACE contains the identifier of a principal, client
   software operated by a human must provide a mechanism for selecting
   this principal.  This specification uses http(s) scheme URLs to
   identify principals, which are represented as WebDAV-capable
   resources.  There is no guarantee that the URLs identifying
   principals will be meaningful to a human.  For example,
   http://www.example.com/u/256432 and
   http://www.example.com/people/Greg.Stein are both valid URLs that
   could be used to identify the same principal.  To remedy this, every
   principal resource has the DAV:displayname property containing a
   human-readable name for the principal.

   Since a principal can be identified by multiple URLs, it raises the
   problem of determining exactly which principal is being referenced in
   a given ACE.  It is impossible for a client to determine that an ACE
   granting the read privilege to http://www.example.com/people/
   Greg.Stein also affects the principal at http://www.example.com/u/
   256432.  That is, a client has no mechanism for determining that two

   URLs identify the same principal resource.  As a result, this
   specification requires clients to use just one of the many possible
   URLs for a principal when creating ACEs.  A client can discover which
   URL to use by retrieving the DAV:principal-URL property (Section 4.2)
   from a principal resource.  No matter which of the principal's URLs
   is used with PROPFIND, the property always returns the same URL.

   With a system having hundreds to thousands of principals, the problem
   arises of how to allow a human operator of client software to select
   just one of these principals.  One approach is to use broad
   collection hierarchies to spread the principals over a large number
   of collections, yielding few principals per collection.  An example
   of this is a two level hierarchy with the first level containing 36
   collections (a-z, 0-9), and the second level being another 36,
   creating collections /a/a/, /a/b/, ..., /a/z/, such that a principal
   with last name "Stein" would appear at /s/t/Stein.  In effect, this
   pre-computes a common query, search on last name, and encodes it into
   a hierarchy.  The drawback with this scheme is that it handles only a
   small set of predefined queries, and drilling down through the
   collection hierarchy adds unnecessary steps (navigate down/up) when
   the user already knows the principal's name.  While organizing
   principal URLs into a hierarchy is a valid namespace organization,
   users should not be forced to navigate this hierarchy to select a
   principal.

   This specification provides the capability to perform substring
   searches over a small set of properties on the resources representing
   principals.  This permits searches based on last name, first name,
   user name, job title, etc.  Two separate searches are supported, both
   via the REPORT method, one to search principal resources
   (DAV:principal-property-search, Section 9.4), the other to determine
   which properties may be searched at all (DAV:principal-search-
   property-set, Section 9.5).

   Once a principal has been identified in an ACE, a server evaluating
   that ACE must know the identity of the principal making a protocol
   request, and must validate that that principal is who they claim to
   be, a process known as authentication.  This specification
   intentionally omits discussion of authentication, as the HTTP
   protocol already has a number of authentication mechanisms [RFC2617].
   Some authentication mechanism (such as HTTP Digest Authentication,
   which all WebDAV compliant implementations are required to support)
   must be available to validate the identity of a principal.

   The following issues are out of scope for this document:

   o  Access control that applies only to a particular property on a
      resource (excepting the access control properties DAV:acl and
      DAV:current-user-privilege-set), rather than the entire resource,

   o  Role-based security (where a role can be seen as a dynamically
      defined group of principals),

   o  Specification of the ways an ACL on a resource is initialized,

   o  Specification of an ACL that applies globally to all resources,
      rather than to a particular resource.

   o  Creation and maintenance of resources representing people or
      computational agents (principals), and groups of these.

   This specification is organized as follows.  Section 1.1 defines key
   concepts used throughout the specification, and is followed by a more
   in-depth discussion of principals (Section 2), and privileges
   (Section 3).  Properties defined on principals are specified in
   Section 4, and access control properties for content resources are
   specified in Section 5.  The ways ACLs are to be evaluated is
   described in Section 6.  Client discovery of access control
   capability using OPTIONS is described in Section 7.2.  Interactions
   between access control functionality and existing HTTP and WebDAV
   methods are described in the remainder of Section 7.  The access
   control setting method, ACL, is specified in Section 8.  Four reports
   that provide limited server-side searching capabilities are described
   in Section 9.  Sections on XML processing (Section 10),
   Internationalization considerations (Section 11), security
   considerations (Section 12), and authentication (Section 13) round
   out the specification.  An appendix (Appendix A) provides an XML
   Document Type Definition (DTD) for the XML elements defined in the
   specification.

1.1.  Terms

   This document uses the terms defined in HTTP [RFC2616] and WebDAV
   [RFC2518].  In addition, the following terms are defined:

   principal

      A "principal" is a distinct human or computational actor that
      initiates access to network resources.  In this protocol, a
      principal is an HTTP resource that represents such an actor.

   group

      A "group" is a principal that represents a set of other
      principals.

   privilege

      A "privilege" controls access to a particular set of HTTP
      operations on a resource.

   aggregate privilege

      An "aggregate privilege" is a privilege that contains a set of
      other privileges.

   abstract privilege

      The modifier "abstract", when applied to a privilege on a
      resource, means the privilege cannot be set in an access control
      element (ACE) on that resource.

   access control list (ACL)

      An "ACL" is a list of access control elements that define access
      control to a particular resource.

   access control element (ACE)

      An "ACE" either grants or denies a particular set of (non-
      abstract) privileges for a particular principal.

   inherited ACE

      An "inherited ACE" is an ACE that is dynamically shared from the
      ACL of another resource.  When a shared ACE changes on the primary
      resource, it is also changed on inheriting resources.

   protected property

      A "protected property" is one whose value cannot be updated except
      by a method explicitly defined as updating that specific property.
      In particular, a protected property cannot be updated with a
      PROPPATCH request.

1.2.  Notational Conventions

   The augmented BNF used by this document to describe protocol elements
   is described in Section 2.1 of [RFC2616].  Because this augmented BNF
   uses the basic production rules provided in Section 2.2 of [RFC2616],
   those rules apply to this document as well.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Definitions of XML elements in this document use XML element type
   declarations (as found in XML Document Type Declarations), described
   in Section 3.2 of [REC-XML].  When an XML element type in the "DAV:"
   namespace is referenced in this document outside of the context of an
   XML fragment, the string "DAV:" will be prefixed to the element name.

2.  Principals

   A principal is a network resource that represents a distinct human or
   computational actor that initiates access to network resources.
   Users and groups are represented as principals in many
   implementations; other types of principals are also possible.  A URI
   of any scheme MAY be used to identify a principal resource.  However,
   servers implementing this specification MUST expose principal
   resources at an http(s) URL, which is a privileged scheme that points
   to resources that have additional properties, as described in Section
   4.  So, a principal resource can have multiple URIs, one of which has
   to be an http(s) scheme URL.  Although an implementation SHOULD
   support PROPFIND and MAY support PROPPATCH to access and modify
   information about a principal, it is not required to do so.

   A principal resource may be a group, where a group is a principal
   that represents a set of other principals, called the members of the
   group.  If a person or computational agent matches a principal
   resource that is a member of a group, they also match the group.
   Membership in a group is recursive, so if a principal is a member of
   group GRPA, and GRPA is a member of group GRPB, then the principal is
   also a member of GRPB.

3.  Privileges

   Ability to perform a given method on a resource MUST be controlled by
   one or more privileges.  Authors of protocol extensions that define
   new HTTP methods SHOULD specify which privileges (by defining new
   privileges, or mapping to ones below) are required to perform the
   method.  A principal with no privileges to a resource MUST be denied
   any HTTP access to that resource, unless the principal matches an ACE

   constructed using the DAV:all, DAV:authenticated, or
   DAV:unauthenticated pseudo-principals (see Section 5.5.1).  Servers
   MUST report a 403 "Forbidden" error if access is denied, except in
   the case where the privilege restricts the ability to know the
   resource exists, in which case 404 "Not Found" may be returned.

   Privileges may be containers of other privileges, in which case they
   are termed "aggregate privileges".  If a principal is granted or
   denied an aggregate privilege, it is semantically equivalent to
   granting or denying each of the aggregated privileges individually.
   For example, an implementation may define add-member and remove-
   member privileges that control the ability to add and remove a member
   of a group.  Since these privileges control the ability to update the
   state of a group, these privileges would be aggregated by the
   DAV:write privilege on a group, and granting the DAV:write privilege
   on a group would also grant the add-member and remove-member
   privileges.

   Privileges may be declared to be "abstract" for a given resource, in
   which case they cannot be set in an ACE on that resource.  Aggregate
   and non-aggregate privileges are both capable of being abstract.
   Abstract privileges are useful for modeling privileges that otherwise
   would not be exposed via the protocol.  Abstract privileges also
   provide server implementations with flexibility in implementing the
   privileges defined in this specification.  For example, if a server
   is incapable of separating the read resource capability from the read
   ACL capability, it can still model the DAV:read and DAV:read-acl
   privileges defined in this specification by declaring them abstract,
   and containing them within a non-abstract aggregate privilege (say,
   read-all) that holds DAV:read, and DAV:read-acl.  In this way, it is
   possible to set the aggregate privilege, read-all, thus coupling the
   setting of DAV:read and DAV:read-acl, but it is not possible to set
   DAV:read, or DAV:read-acl individually.  Since aggregate privileges
   can be abstract, it is also possible to use abstract privileges to
   group or organize non-abstract privileges.  Privilege containment
   loops are not allowed; therefore, a privilege MUST NOT contain
   itself.  For example, DAV:read cannot contain DAV:read.

   The set of privileges that apply to a particular resource may vary
   with the DAV:resourcetype of the resource, as well as between
   different server implementations.  To promote interoperability,
   however, this specification defines a set of well-known privileges
   (e.g., DAV:read, DAV:write, DAV:read-acl, DAV:write-acl, DAV:read-
   current-user-privilege-set, and DAV:all), which can at least be used
   to classify the other privileges defined on a particular resource.
   The access permissions on null resources (defined in [RFC2518],
   Section 3) are solely those they inherit (if any), and they are not
   discoverable (i.e., the access control properties specified in

   Section 5 are not defined on null resources).  On the transition from
   null to stateful resource, the initial access control list is set by
   the server's default ACL value policy (if any).

   Server implementations MAY define new privileges beyond those defined
   in this specification.  Privileges defined by individual
   implementations MUST NOT use the DAV: namespace, and instead should
   use a namespace that they control, such as an http scheme URL.

3.1.  DAV:read Privilege

   The read privilege controls methods that return information about the
   state of the resource, including the resource's properties.  Affected
   methods include GET and PROPFIND.  Any implementation-defined
   privilege that also controls access to GET and PROPFIND must be
   aggregated under DAV:read - if an ACL grants access to DAV:read, the
   client may expect that no other privilege needs to be granted to have
   access to GET and PROPFIND.  Additionally, the read privilege MUST
   control the OPTIONS method.

   <!ELEMENT read EMPTY>

3.2.  DAV:write Privilege

   The write privilege controls methods that lock a resource or modify
   the content, dead properties, or (in the case of a collection)
   membership of the resource, such as PUT and PROPPATCH.  Note that
   state modification is also controlled via locking (see section 5.3 of
   [RFC2518]), so effective write access requires that both write
   privileges and write locking requirements are satisfied.  Any
   implementation-defined privilege that also controls access to methods
   modifying content, dead properties or collection membership must be
   aggregated under DAV:write, e.g., if an ACL grants access to
   DAV:write, the client may expect that no other privilege needs to be
   granted to have access to PUT and PROPPATCH.

   <!ELEMENT write EMPTY>

3.3.  DAV:write-properties Privilege

   The DAV:write-properties privilege controls methods that modify the
   dead properties of the resource, such as PROPPATCH.  Whether this
   privilege may be used to control access to any live properties is
   determined by the implementation.  Any implementation-defined
   privilege that also controls access to methods modifying dead
   properties must be aggregated under DAV:write-properties - e.g., if

   an ACL grants access to DAV:write-properties, the client can safely
   expect that no other privilege needs to be granted to have access to
   PROPPATCH.

   <!ELEMENT write-properties EMPTY>

3.4.  DAV:write-content Privilege

   The DAV:write-content privilege controls methods that modify the
   content of an existing resource, such as PUT.  Any implementation-
   defined privilege that also controls access to content must be
   aggregated under DAV:write-content - e.g., if an ACL grants access to
   DAV:write-content, the client can safely expect that no other
   privilege needs to be granted to have access to PUT.  Note that PUT -
   when applied to an unmapped URI - creates a new resource and
   therefore is controlled by the DAV:bind privilege on the parent
   collection.

   <!ELEMENT write-content EMPTY>

3.5.  DAV:unlock Privilege

   The DAV:unlock privilege controls the use of the UNLOCK method by a
   principal other than the lock owner (the principal that created a
   lock can always perform an UNLOCK).  While the set of users who may
   lock a resource is most commonly the same set of users who may modify
   a resource, servers may allow various kinds of administrators to
   unlock resources locked by others.  Any privilege controlling access
   by non-lock owners to UNLOCK MUST be aggregated under DAV:unlock.

   A lock owner can always remove a lock by issuing an UNLOCK with the
   correct lock token and authentication credentials.  That is, even if
   a principal does not have DAV:unlock privilege, they can still remove
   locks they own.  Principals other than the lock owner can remove a
   lock only if they have DAV:unlock privilege and they issue an UNLOCK
   with the correct lock token.  Lock timeout is not affected by the
   DAV:unlock privilege.

   <!ELEMENT unlock EMPTY>

3.6.  DAV:read-acl Privilege

   The DAV:read-acl privilege controls the use of PROPFIND to retrieve
   the DAV:acl property of the resource.

   <!ELEMENT read-acl EMPTY>

3.7.  DAV:read-current-user-privilege-set Privilege

   The DAV:read-current-user-privilege-set privilege controls the use of
   PROPFIND to retrieve the DAV:current-user-privilege-set property of
   the resource.

   Clients are intended to use this property to visually indicate in
   their UI items that are dependent on the permissions of a resource,
   for example, by graying out resources that are not writable.

   This privilege is separate from DAV:read-acl because there is a need
   to allow most users access to the privileges permitted the current
   user (due to its use in creating the UI), while the full ACL contains
   information that may not be appropriate for the current authenticated
   user.  As a result, the set of users who can view the full ACL is
   expected to be much smaller than those who can read the current user
   privilege set, and hence distinct privileges are needed for each.

   <!ELEMENT read-current-user-privilege-set EMPTY>

3.8.  DAV:write-acl Privilege

   The DAV:write-acl privilege controls use of the ACL method to modify
   the DAV:acl property of the resource.

   <!ELEMENT write-acl EMPTY>

3.9.  DAV:bind Privilege

   The DAV:bind privilege allows a method to add a new member URL to the
   specified collection (for example via PUT or MKCOL).  It is ignored
   for resources that are not collections.

   <!ELEMENT bind EMPTY>

3.10.  DAV:unbind Privilege

   The DAV:unbind privilege allows a method to remove a member URL from
   the specified collection (for example via DELETE or MOVE).  It is
   ignored for resources that are not collections.

   <!ELEMENT unbind EMPTY>

3.11.  DAV:all Privilege

   DAV:all is an aggregate privilege that contains the entire set of
   privileges that can be applied to the resource.

   <!ELEMENT all EMPTY>

3.12.  Aggregation of Predefined Privileges

   Server implementations are free to aggregate the predefined
   privileges (defined above in Sections 3.1-3.10) subject to the
   following limitations:

   DAV:read-acl MUST NOT contain DAV:read, DAV:write, DAV:write-acl,
   DAV:write-properties, DAV:write-content, or DAV:read-current-user-
   privilege-set.

   DAV:write-acl MUST NOT contain DAV:write, DAV:read, DAV:read-acl, or
   DAV:read-current-user-privilege-set.

   DAV:read-current-user-privilege-set MUST NOT contain DAV:write,
   DAV:read, DAV:read-acl, or DAV:write-acl.

   DAV:write MUST NOT contain DAV:read, DAV:read-acl, or DAV:read-
   current-user-privilege-set.

   DAV:read MUST NOT contain DAV:write, DAV:write-acl, DAV:write-
   properties, or DAV:write-content.

   DAV:write MUST contain DAV:bind, DAV:unbind, DAV:write-properties and
   DAV:write-content.

4.  Principal Properties

   Principals are manifested to clients as a WebDAV resource, identified
   by a URL.  A principal MUST have a non-empty DAV:displayname property
   (defined in Section 13.2 of [RFC2518]), and a DAV:resourcetype
   property (defined in Section 13.9 of [RFC2518]).  Additionally, a
   principal MUST report the DAV:principal XML element in the value of
   the DAV:resourcetype property.  The element type declaration for
   DAV:principal is:

   <!ELEMENT principal EMPTY>

   This protocol defines the following additional properties for a
   principal.  Since it can be expensive for a server to retrieve access
   control information, the name and value of these properties SHOULD
   NOT be returned by a PROPFIND allprop request (as defined in Section
   12.14.1 of [RFC2518]).

4.1.  DAV:alternate-URI-set

   This protected property, if non-empty, contains the URIs of network
   resources with additional descriptive information about the
   principal.  This property identifies additional network resources
   (i.e., it contains one or more URIs) that may be consulted by a
   client to gain additional knowledge concerning a principal.  One
   expected use for this property is the storage of an LDAP [RFC2255]
   scheme URL.  A user-agent encountering an LDAP URL could use LDAP
   [RFC2251] to retrieve additional machine-readable directory
   information about the principal, and display that information in its
   user interface.  Support for this property is REQUIRED, and the value
   is empty if no alternate URI exists for the principal.

   <!ELEMENT alternate-URI-set (href*)>

4.2.  DAV:principal-URL

   A principal may have many URLs, but there must be one "principal URL"
   that clients can use to uniquely identify a principal.  This
   protected property contains the URL that MUST be used to identify
   this principal in an ACL request.  Support for this property is
   REQUIRED.

   <!ELEMENT principal-URL (href)>

4.3.  DAV:group-member-set

   This property of a group principal identifies the principals that are
   direct members of this group.  Since a group may be a member of
   another group, a group may also have indirect members (i.e., the
   members of its direct members).  A URL in the DAV:group-member-set
   for a principal MUST be the DAV:principal-URL of that principal.

   <!ELEMENT group-member-set (href*)>

4.4.  DAV:group-membership

   This protected property identifies the groups in which the principal
   is directly a member.  Note that a server may allow a group to be a
   member of another group, in which case the DAV:group-membership of

   those other groups would need to be queried in order to determine the
   groups in which the principal is indirectly a member.  Support for
   this property is REQUIRED.

   <!ELEMENT group-membership (href*)>

5.  Access Control Properties

   This specification defines a number of new properties for WebDAV
   resources.  Access control properties may be retrieved just like
   other WebDAV properties, using the PROPFIND method.  Since it is
   expensive, for many servers, to retrieve access control information,
   a PROPFIND allprop request (as defined in Section 12.14.1 of
   [RFC2518]) SHOULD NOT return the names and values of the properties
   defined in this section.

   Access control properties (especially DAV:acl and DAV:inherited-acl-
   set) are defined on the resource identified by the Request-URI of a
   PROPFIND request.  A direct consequence is that if the resource is
   accessible via multiple URI, the value of access control properties
   is the same across these URI.

   HTTP resources that support the WebDAV Access Control Protocol MUST
   contain the following properties.  Null resources (described in
   Section 3 of [RFC2518]) MUST NOT contain the following properties.

5.1.  DAV:owner

   This  property identifies a particular principal as being the "owner"
   of the resource.  Since the owner of a resource often has special
   access control capabilities (e.g., the owner frequently has permanent
   DAV:write-acl privilege), clients might display the resource owner in
   their user interface.

   Servers MAY implement DAV:owner as protected property and MAY return
   an empty DAV:owner element as property value in case no owner
   information is available.

   <!ELEMENT owner (href?)>

5.1.1.  Example: Retrieving DAV:owner

   This example shows a client request for the value of the DAV:owner
   property from a collection resource with URL http://www.example.com/
   papers/.  The principal making the request is authenticated using
   Digest authentication.  The value of DAV:owner is the URL http://
   www.example.com/acl/users/gstein, wrapped in the DAV:href XML
   element.

   >> Request <<

   PROPFIND /papers/ HTTP/1.1
   Host: www.example.com
   Content-type: text/xml; charset="utf-8"
   Content-Length: xxx
   Depth: 0
   Authorization: Digest username="jim",
     realm="users@example.com", nonce="...",
     uri="/papers/", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:prop>
       <D:owner/>
     </D:prop>
   </D:propfind>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.example.com/papers/</D:href>
       <D:propstat>
         <D:prop>
           <D:owner>
             <D:href>http://www.example.com/acl/users/gstein</D:href>
           </D:owner>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

5.1.2.  Example: An Attempt to Set DAV:owner

   The following example shows a client request to modify the value of
   the DAV:owner property on the resource with URL <http://
   www.example.com/papers>.  Since DAV:owner is a protected property on
   this particular server, it responds with a 207 (Multi-Status)
   response that contains a 403 (Forbidden) status code for the act of
   setting DAV:owner.  Section 8.2.1 of [RFC2518] describes PROPPATCH
   status code information,  Section 11 of [RFC2518] describes the

   Multi-Status response and Sections 1.6 and 3.12 of [RFC3253] describe
   additional error marshaling for PROPPATCH attempts on protected
   properties.

   >> Request <<

   PROPPATCH /papers/ HTTP/1.1
   Host: www.example.com
   Content-type: text/xml; charset="utf-8"
   Content-Length: xxx
   Depth: 0
   Authorization: Digest username="jim",
     realm="users@example.com", nonce="...",
     uri="/papers/", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propertyupdate xmlns:D="DAV:">
     <D:set>
       <D:prop>
         <D:owner>
           <D:href>http://www.example.com/acl/users/jim</D:href>
         </D:owner>
       </D:prop>
     </D:set>
   </D:propertyupdate>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.example.com/papers/</D:href>
       <D:propstat>
         <D:prop><D:owner/></D:prop>
         <D:status>HTTP/1.1 403 Forbidden</D:status>
         <D:responsedescription>
           <D:error><D:cannot-modify-protected-property/></D:error>
           Failure to set protected property (DAV:owner)
         </D:responsedescription>
       </D:propstat>
     </D:response>
   </D:multistatus>

5.2.  DAV:group

   This property identifies a particular principal as being the "group"
   of the resource.  This property is commonly found on repositories
   that implement the Unix privileges model.

   Servers MAY implement DAV:group as protected property and MAY return
   an empty DAV:group element as property value in case no group
   information is available.

   <!ELEMENT group (href?)>

5.3.  DAV:supported-privilege-set

   This is a protected property that identifies the privileges defined
   for the resource.

   <!ELEMENT supported-privilege-set (supported-privilege*)>

   Each privilege appears as an XML element, where aggregate privileges
   list as sub-elements all of the privileges that they aggregate.

   <!ELEMENT supported-privilege
    (privilege, abstract?, description, supported-privilege*)>
   <!ELEMENT privilege ANY>

   An abstract privilege MUST NOT be used in an ACE for that resource.
   Servers MUST fail an attempt to set an abstract privilege.

   <!ELEMENT abstract EMPTY>

   A description is a human-readable description of what this privilege
   controls access to.  Servers MUST indicate the human language of the
   description using the xml:lang attribute and SHOULD consider the HTTP
   Accept-Language request header when selecting one of multiple
   available languages.

   <!ELEMENT description #PCDATA>

   It is envisioned that a WebDAV ACL-aware administrative client would
   list the supported privileges in a dialog box, and allow the user to
   choose non-abstract privileges to apply in an ACE.  The privileges
   tree is useful programmatically to map well-known privileges (defined
   by WebDAV or other standards groups) into privileges that are
   supported by any particular server implementation.  The privilege
   tree also serves to hide complexity in implementations allowing large
   number of privileges to be defined by displaying aggregates to the
   user.

5.3.1.  Example: Retrieving a List of Privileges Supported on a Resource

   This example shows a client request for the DAV:supported-privilege-
   set property on the resource http://www.example.com/papers/.  The
   value of the DAV:supported-privilege-set property is a tree of
   supported privileges (using "[XML Namespace , localname]" to identify
   each privilege):

   [DAV:, all] (aggregate, abstract)
      |
      +-- [DAV:, read] (aggregate)
             |
             +-- [DAV:, read-acl] (abstract)
             +-- [DAV:, read-current-user-privilege-set] (abstract)
      |
      +-- [DAV:, write] (aggregate)
             |
             +-- [DAV:, write-acl] (abstract)
             +-- [DAV:, write-properties]
             +-- [DAV:, write-content]
      |
      +-- [DAV:, unlock]

   This privilege tree is not normative (except that it reflects the
   normative aggregation rules given in Section 3.12), and many possible
   privilege trees are possible.

   >> Request <<

   PROPFIND /papers/ HTTP/1.1
   Host: www.example.com
   Content-type: text/xml; charset="utf-8"
   Content-Length: xxx
   Depth: 0
   Authorization: Digest username="gclemm",
     realm="users@example.com", nonce="...",
     uri="/papers/", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:prop>
       <D:supported-privilege-set/>
     </D:prop>
   </D:propfind>

   >> Response <<

   HTTP/1.1 207 Multi-Status

   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.example.com/papers/</D:href>
       <D:propstat>
         <D:prop>
           <D:supported-privilege-set>
             <D:supported-privilege>
               <D:privilege><D:all/></D:privilege>
              <D:abstract/>
               <D:description xml:lang="en">
                 Any operation
               </D:description>
               <D:supported-privilege>
                 <D:privilege><D:read/></D:privilege>
                 <D:description xml:lang="en">
                   Read any object
                 </D:description>
                 <D:supported-privilege>
                   <D:privilege><D:read-acl/></D:privilege>
                   <D:abstract/>
                   <D:description xml:lang="en">Read ACL</D:description>
                 </D:supported-privilege>
                 <D:supported-privilege>
                   <D:privilege>
                     <D:read-current-user-privilege-set/>
                   </D:privilege>
                   <D:abstract/>
                   <D:description xml:lang="en">
                     Read current user privilege set property
                   </D:description>
                 </D:supported-privilege>
               </D:supported-privilege>
               <D:supported-privilege>
                 <D:privilege><D:write/></D:privilege>
                 <D:description xml:lang="en">
                   Write any object
                 </D:description>
                 <D:supported-privilege>
                   <D:privilege><D:write-acl/></D:privilege>
                   <D:description xml:lang="en">

                     Write ACL
                   </D:description>
                   <D:abstract/>
                 </D:supported-privilege>
                 <D:supported-privilege>
                   <D:privilege><D:write-properties/></D:privilege>
                   <D:description xml:lang="en">
                     Write properties
                   </D:description>
                 </D:supported-privilege>
                 <D:supported-privilege>
                   <D:privilege><D:write-content/></D:privilege>
                   <D:description xml:lang="en">
                     Write resource content
                   </D:description>
                 </D:supported-privilege>
               </D:supported-privilege>
               <D:supported-privilege>
                 <D:privilege><D:unlock/></D:privilege>
                 <D:description xml:lang="en">
                   Unlock resource
                 </D:description>
               </D:supported-privilege>
             </D:supported-privilege>
           </D:supported-privilege-set>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

5.4.  DAV:current-user-privilege-set

   DAV:current-user-privilege-set is a protected property containing the
   exact set of privileges (as computed by the server) granted to the
   currently authenticated HTTP user.  Aggregate privileges and their
   contained privileges are listed.  A user-agent can use the value of
   this property to adjust its user interface to make actions
   inaccessible (e.g., by graying out a menu item or button) for which
   the current principal does not have permission.  This property is
   also useful for determining what operations the current principal can
   perform, without having to actually execute an operation.

   <!ELEMENT current-user-privilege-set (privilege*)>
   <!ELEMENT privilege ANY>

   If the current user is granted a specific privilege, that privilege
   must belong to the set of privileges that may be set on this
   resource.  Therefore, each element in the DAV:current-user-
   privilege-set property MUST identify a non-abstract privilege from
   the DAV:supported-privilege-set property.

5.4.1.  Example: Retrieving the User's Current Set of Assigned
        Privileges

   Continuing the example from Section 5.3.1, this example shows a
   client requesting the DAV:current-user-privilege-set property from
   the resource with URL http://www.example.com/papers/.  The username
   of the principal making the request is "khare", and Digest
   authentication is used in the request.  The principal with username
   "khare" has been granted the DAV:read privilege.  Since the DAV:read
   privilege contains the DAV:read-acl and DAV:read-current-user-
   privilege-set privileges (see Section 5.3.1), the principal with
   username "khare" can read the ACL property, and the DAV:current-
   user-privilege-set property.  However, the DAV:all, DAV:read-acl,
   DAV:write-acl and DAV:read-current-user-privilege-set privileges are
   not listed in the value of DAV:current-user-privilege-set, since (for
   this example) they are abstract privileges.  DAV:write is not listed
   since the principal with username "khare" is not listed in an ACE
   granting that principal write permission.

   >> Request <<

   PROPFIND /papers/ HTTP/1.1
   Host: www.example.com
   Content-type: text/xml; charset="utf-8"
   Content-Length: xxx
   Depth: 0
   Authorization: Digest username="khare",
     realm="users@example.com", nonce="...",
     uri="/papers/", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:prop>
       <D:current-user-privilege-set/>
     </D:prop>
   </D:propfind>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
     <D:href>http://www.example.com/papers/</D:href>
     <D:propstat>
       <D:prop>
         <D:current-user-privilege-set>
           <D:privilege><D:read/></D:privilege>
         </D:current-user-privilege-set>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
     </D:response>
   </D:multistatus>

5.5.  DAV:acl

   This is a protected property that specifies the list of access
   control entries (ACEs), which define what principals are to get what
   privileges for this resource.

   <!ELEMENT acl (ace*) >

   Each DAV:ace element specifies the set of privileges to be either
   granted or denied to a single principal.  If the DAV:acl property is
   empty, no principal is granted any privilege.

   <!ELEMENT ace ((principal | invert), (grant|deny), protected?,
                  inherited?)>

5.5.1.  ACE Principal

   The DAV:principal element identifies the principal to which this ACE
   applies.

   <!ELEMENT principal (href | all | authenticated | unauthenticated
    | property | self)>

   The current user matches DAV:href only if that user is authenticated
   as being (or being a member of) the principal identified by the URL
   contained by that DAV:href.

   The current user always matches DAV:all.

   <!ELEMENT all EMPTY>

   The current user matches DAV:authenticated only if authenticated.

   <!ELEMENT authenticated EMPTY>

   The current user matches DAV:unauthenticated only if not
   authenticated.

   <!ELEMENT unauthenticated EMPTY>

   DAV:all is the union of DAV:authenticated, and DAV:unauthenticated.
   For a given request, the user matches either DAV:authenticated, or
   DAV:unauthenticated, but not both (that is, DAV:authenticated and
   DAV:unauthenticated are disjoint sets).

   The current user matches a DAV:property principal in a DAV:acl
   property of a resource only if the value of the identified property
   of that resource contains at most one DAV:href XML element, the URI
   value of DAV:href identifies a principal, and the current user is
   authenticated as being (or being a member of) that principal.  For
   example, if the DAV:property element contained <DAV:owner/>, the
   current user would match the DAV:property principal only if the
   current user is authenticated as matching the principal identified by
   the DAV:owner property of the resource.

   <!ELEMENT property ANY>

   The current user matches DAV:self in a DAV:acl property of the
   resource only if that resource is a principal and that principal
   matches the current user or, if the principal is a group, a member of
   that group matches the current user.

   <!ELEMENT self EMPTY>

   Some servers may support ACEs applying to those users NOT matching
   the current principal, e.g., all users not in a particular group.
   This can be done by wrapping the DAV:principal element with
   DAV:invert.

   <!ELEMENT invert principal>

5.5.2.  ACE Grant and Deny

   Each DAV:grant or DAV:deny element specifies the set of privileges to
   be either granted or denied to the specified principal.  A DAV:grant
   or DAV:deny element of the DAV:acl of a resource MUST only contain
   non-abstract elements specified in the DAV:supported-privilege-set of
   that resource.

   <!ELEMENT grant (privilege+)>
   <!ELEMENT deny (privilege+)>
   <!ELEMENT privilege ANY>

5.5.3.  ACE Protection

   A server indicates an ACE is protected by including the DAV:protected
   element in the ACE.  If the ACL of a resource contains an ACE with a
   DAV:protected element, an attempt to remove that ACE from the ACL
   MUST fail.

   <!ELEMENT protected EMPTY>

5.5.4.  ACE Inheritance

   The presence of a DAV:inherited element indicates that this ACE is
   inherited from another resource that is identified by the URL
   contained in a DAV:href element.  An inherited ACE cannot be modified
   directly, but instead the ACL on the resource from which it is
   inherited must be modified.

   Note that ACE inheritance is not the same as ACL initialization.  ACL
   initialization defines the ACL that a newly created resource will use
   (if not specified).  ACE inheritance refers to an ACE that is
   logically shared - where an update to the resource containing an ACE
   will affect the ACE of each resource that inherits that ACE.  The
   method by which ACLs are initialized or by which ACEs are inherited
   is not defined by this document.

   <!ELEMENT inherited (href)>

5.5.5.  Example: Retrieving a Resource's Access Control List

   Continuing the example from Sections 5.3.1 and 5.4.1, this example
   shows a client requesting the DAV:acl property from the resource with
   URL http://www.example.com/papers/.  There are two ACEs defined in
   this ACL:

   ACE #1: The group identified by URL http://www.example.com/acl/
   groups/maintainers (the group of site maintainers) is granted
   DAV:write privilege.  Since (for this example) DAV:write contains the
   DAV:write-acl privilege (see Section 5.3.1), this means the
   "maintainers" group can also modify the access control list.

   ACE #2: All principals (DAV:all) are granted the DAV:read privilege.
   Since (for this example) DAV:read contains DAV:read-acl and
   DAV:read-current-user-privilege-set, this means all users (including
   all members of the "maintainers" group) can read the DAV:acl property
   and the DAV:current-user-privilege-set property.

   >> Request <<

   PROPFIND /papers/ HTTP/1.1
   Host: www.example.com
   Content-type: text/xml; charset="utf-8"
   Content-Length: xxx
   Depth: 0
   Authorization: Digest username="masinter",
     realm="users@example.com", nonce="...",
     uri="/papers/", response="...", opaque="..."

   <D:propfind xmlns:D="DAV:">
     <D:prop>
       <D:acl/>
     </D:prop>
   </D:propfind>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.example.com/papers/</D:href>
       <D:propstat>
         <D:prop>
           <D:acl>
           <D:ace>
             <D:principal>
               <D:href
               >http://www.example.com/acl/groups/maintainers</D:href>
             </D:principal>
             <D:grant>
               <D:privilege><D:write/></D:privilege>

             </D:grant>
           </D:ace>
           <D:ace>
             <D:principal>
               <D:all/>
             </D:principal>
             <D:grant>
               <D:privilege><D:read/></D:privilege>
             </D:grant>
           </D:ace>
         </D:acl>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

5.6.  DAV:acl-restrictions

   This protected property defines the types of ACLs supported by this
   server, to avoid clients needlessly getting errors.  When a client
   tries to set an ACL via the ACL method, the server may reject the
   attempt to set the ACL as specified.  The following properties
   indicate the restrictions the client must observe before setting an
   ACL:

   <grant-only> Deny ACEs are not supported

   <no-invert> Inverted ACEs are not supported

   <deny-before-grant> All deny ACEs must occur before any grant ACEs

   <required-principal> Indicates which principals are required to be
      present

   <!ELEMENT acl-restrictions (grant-only?, no-invert?,
                               deny-before-grant?,
                               required-principal?)>

5.6.1.  DAV:grant-only

   This element indicates that ACEs with deny clauses are not allowed.

   <!ELEMENT grant-only EMPTY>

5.6.2.  DAV:no-invert ACE Constraint

   This element indicates that ACEs with the <invert> element are not
   allowed.

   <!ELEMENT no-invert EMPTY>

5.6.3.  DAV:deny-before-grant

   This element indicates that all deny ACEs must precede all grant
   ACEs.

   <!ELEMENT deny-before-grant EMPTY>

5.6.4.  Required Principals

   The required principal elements identify which principals must have
   an ACE defined in the ACL.

   <!ELEMENT required-principal
     (all? | authenticated? | unauthenticated? | self? | href* |
      property*)>

   For example, the following element requires that the ACL contain a

   DAV:owner property ACE:

   <D:required-principal xmlns:D="DAV:">
     <D:property><D:owner/></D:property>
   </D:required-principal>

5.6.5.  Example: Retrieving DAV:acl-restrictions

   In this example, the client requests the value of the DAV:acl-
   restrictions property.  Digest authentication provides credentials
   for the principal operating the client.

   >> Request <<

   PROPFIND /papers/ HTTP/1.1
   Host: www.example.com
   Content-type: text/xml; charset="utf-8"
   Content-Length: xxx
   Depth: 0
   Authorization: Digest username="srcarter",
     realm="users@example.com", nonce="...",
     uri="/papers/", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:prop>
       <D:acl-restrictions/>
     </D:prop>
   </D:propfind>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.example.com/papers/</D:href>
       <D:propstat>
         <D:prop>
           <D:acl-restrictions>
             <D:grant-only/>
             <D:required-principal>
               <D:all/>
             </D:required-principal>
           </D:acl-restrictions>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

5.7.  DAV:inherited-acl-set

   This protected property contains a set of URLs that identify other
   resources that also control the access to this resource.  To have a
   privilege on a resource, not only must the ACL on that resource
   (specified in the DAV:acl property of that resource) grant the
   privilege, but so must the ACL of each resource identified in the
   DAV:inherited-acl-set property of that resource.  Effectively, the
   privileges granted by the current ACL are ANDed with the privileges
   granted by each inherited ACL.

   <!ELEMENT inherited-acl-set (href*)>

5.8.  DAV:principal-collection-set

   This protected property of a resource contains a set of URLs that
   identify the root collections that contain the principals that are
   available on the server that implements this resource.  A WebDAV
   Access Control Protocol user agent could use the contents of
   DAV:principal-collection-set to retrieve the DAV:displayname property
   (specified in Section 13.2 of [RFC2518]) of all principals on that
   server, thereby yielding human-readable names for each principal that
   could be displayed in a user interface.

   <!ELEMENT principal-collection-set (href*)>

   Since different servers can control different parts of the URL
   namespace, different resources on the same host MAY have different
   DAV:principal-collection-set values.  The collections specified in
   the DAV:principal-collection-set MAY be located on different hosts
   from the resource. The URLs in DAV:principal-collection-set SHOULD be
   http or https scheme URLs.  For security and scalability reasons, a
   server MAY report only a subset of the entire set of known principal
   collections, and therefore clients should not assume they have
   retrieved an exhaustive listing.  Additionally, a server MAY elect to
   report none of the principal collections it knows about, in which
   case the property value would be empty.

   The value of DAV:principal-collection-set gives the scope of the
   DAV:principal-property-search REPORT (defined in Section 9.4).
   Clients use the DAV:principal-property-search REPORT to populate
   their user interface with a list of principals.  Therefore, servers
   that limit a client's ability to obtain principal information will
   interfere with the client's ability to manipulate access control
   lists, due to the difficulty of getting the URL of a principal for
   use in an ACE.

5.8.1.  Example: Retrieving DAV:principal-collection-set

   In this example, the client requests the value of the DAV:principal-
   collection-set property on the collection resource identified by URL
   http://www.example.com/papers/.  The property contains the two URLs,
   http://www.example.com/acl/users/ and http://
   www.example.com/acl/groups/, both wrapped in DAV:href XML elements.
   Digest authentication provides credentials for the principal
   operating the client.

   The client might reasonably follow this request with two separate
   PROPFIND requests to retrieve the DAV:displayname property of the
   members of the two collections (/acl/users and /acl/groups).  This
   information could be used when displaying a user interface for
   creating access control entries.

   >> Request <<

   PROPFIND /papers/ HTTP/1.1
   Host: www.example.com
   Content-type: text/xml; charset="utf-8"
   Content-Length: xxx
   Depth: 0
   Authorization: Digest username="yarong",
     realm="users@example.com", nonce="...",
     uri="/papers/", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:prop>
       <D:principal-collection-set/>
     </D:prop>
   </D:propfind>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.example.com/papers/</D:href>
       <D:propstat>
         <D:prop>
           <D:principal-collection-set>
             <D:href>http://www.example.com/acl/users/</D:href>
             <D:href>http://www.example.com/acl/groups/</D:href>
           </D:principal-collection-set>
         </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

5.9.  Example: PROPFIND to retrieve access control properties

   The following example shows how access control information can be
   retrieved by using the PROPFIND method to fetch the values of the
   DAV:owner, DAV:supported-privilege-set, DAV:current-user-privilege-
   set, and DAV:acl properties.

   >> Request <<

   PROPFIND /top/container/ HTTP/1.1
   Host: www.example.com
   Content-type: text/xml; charset="utf-8"
   Content-Length: xxx
   Depth: 0
   Authorization: Digest username="ejw",
     realm="users@example.com", nonce="...",
     uri="/top/container/", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:prop>
       <D:owner/>
       <D:supported-privilege-set/>
       <D:current-user-privilege-set/>
       <D:acl/>
     </D:prop>
   </D:propfind>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:"
                  xmlns:A="http://www.example.com/acl/">
     <D:response>
       <D:href>http://www.example.com/top/container/</D:href>
       <D:propstat>
         <D:prop>
           <D:owner>
             <D:href>http://www.example.com/users/gclemm</D:href>
           </D:owner>
           <D:supported-privilege-set>
             <D:supported-privilege>
               <D:privilege><D:all/></D:privilege>
               <D:abstract/>

               <D:description xml:lang="en">
                 Any operation
               </D:description>
               <D:supported-privilege>
                 <D:privilege><D:read/></D:privilege>
                 <D:description xml:lang="en">
                   Read any object
                 </D:description>
               </D:supported-privilege>
               <D:supported-privilege>
                 <D:privilege><D:write/></D:privilege>
                 <D:abstract/>
                 <D:description xml:lang="en">
                   Write any object
                 </D:description>
                 <D:supported-privilege>
                   <D:privilege><A:create/></D:privilege>
                   <D:description xml:lang="en">
                     Create an object
                   </D:description>
                 </D:supported-privilege>
                 <D:supported-privilege>
                   <D:privilege><A:update/></D:privilege>
                   <D:description xml:lang="en">
                     Update an object
                   </D:description>
                 </D:supported-privilege>
               </D:supported-privilege>
               <D:supported-privilege>
                 <D:privilege><A:delete/></D:privilege>
                 <D:description xml:lang="en">
                   Delete an object
                 </D:description>
               </D:supported-privilege>
               <D:supported-privilege>
                 <D:privilege><D:read-acl/></D:privilege>
                 <D:description xml:lang="en">
                   Read the ACL
                 </D:description>
               </D:supported-privilege>
               <D:supported-privilege>
                 <D:privilege><D:write-acl/></D:privilege>
                 <D:description xml:lang="en">
                   Write the ACL
                 </D:description>
               </D:supported-privilege>
             </D:supported-privilege>
           </D:supported-privilege-set>

           <D:current-user-privilege-set>
             <D:privilege><D:read/></D:privilege>
             <D:privilege><D:read-acl/></D:privilege>
           </D:current-user-privilege-set>
           <D:acl>
             <D:ace>
               <D:principal>
                 <D:href>http://www.example.com/users/esedlar</D:href>
               </D:principal>
               <D:grant>
                 <D:privilege><D:read/></D:privilege>
                 <D:privilege><D:write/></D:privilege>
                 <D:privilege><D:read-acl/></D:privilege>
               </D:grant>
             </D:ace>
             <D:ace>
               <D:principal>
                 <D:href>http://www.example.com/groups/mrktng</D:href>
               </D:principal>
               <D:deny>
                 <D:privilege><D:read/></D:privilege>
               </D:deny>
             </D:ace>
             <D:ace>
               <D:principal>
                 <D:property><D:owner/></D:property>
               </D:principal>
               <D:grant>
                 <D:privilege><D:read-acl/></D:privilege>
                 <D:privilege><D:write-acl/></D:privilege>
               </D:grant>
             </D:ace>
             <D:ace>
               <D:principal><D:all/></D:principal>
               <D:grant>
                 <D:privilege><D:read/></D:privilege>
               </D:grant>
               <D:inherited>
                 <D:href>http://www.example.com/top</D:href>
               </D:inherited>
             </D:ace>
           </D:acl>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

   The value of the DAV:owner property is a single DAV:href XML element
   containing the URL of the principal that owns this resource.

   The value of the DAV:supported-privilege-set property is a tree of
   supported privileges (using "[XML Namespace , localname]" to identify
   each privilege):

   [DAV:, all] (aggregate, abstract)
      |
      +-- [DAV:, read]
      +-- [DAV:, write] (aggregate, abstract)
             |
             +-- [http://www.example.com/acl, create]
             +-- [http://www.example.com/acl, update]
             +-- [http://www.example.com/acl, delete]
      +-- [DAV:, read-acl]
      +-- [DAV:, write-acl]

   The DAV:current-user-privilege-set property contains two privileges,
   DAV:read, and DAV:read-acl.  This indicates that the current
   authenticated user only has the ability to read the resource, and
   read the DAV:acl property on the resource.  The DAV:acl property
   contains a set of four ACEs:

   ACE #1: The principal identified by the URL http://www.example.com/
   users/esedlar is granted the DAV:read, DAV:write, and DAV:read-acl
   privileges.

   ACE #2: The principals identified by the URL http://www.example.com/
   groups/mrktng are denied the DAV:read privilege.  In this example,
   the principal URL identifies a group.

   ACE #3: In this ACE, the principal is a property principal,
   specifically the DAV:owner property.  When evaluating this ACE, the
   value of the DAV:owner property is retrieved, and is examined to see
   if it contains a DAV:href XML element.  If so, the URL within the
   DAV:href element is read, and identifies a principal.  In this ACE,
   the owner is granted DAV:read-acl, and DAV:write-acl privileges.

   ACE #4: This ACE grants the DAV:all principal (all users) the
   DAV:read privilege.  This ACE is inherited from the resource http://
   www.example.com/top, the parent collection of this resource.

6.  ACL Evaluation

   WebDAV ACLs are evaluated in similar manner as ACLs on Windows NT and
   in NFSv4 [RFC3530]).  An ACL is evaluated to determine whether or not
   access will be granted for a WebDAV request.  ACEs are maintained in
   a particular order, and are evaluated until all of the permissions
   required by the current request have been granted, at which point the
   ACL evaluation is terminated and access is granted.  If, during ACL
   evaluation, a <deny> ACE (matching the current user) is encountered
   for a privilege which has not yet been granted, the ACL evaluation is
   terminated and access is denied.  Failure to have all required
   privileges granted results in access being denied.

   Note that the semantics of many other existing ACL systems may be
   represented via this mechanism, by mixing deny and grant ACEs.  For
   example, consider the standard "rwx" privilege scheme used by UNIX.
   In this scheme, if the current user is the owner of the file, access
   is granted if the corresponding privilege bit is set and denied if
   not set, regardless of the permissions set on the file's group and
   for the world.  An ACL for UNIX permissions of "r--rw-r--" might be
   constructed like:

   <D:acl>
     <D:ace>
       <D:principal>
         <D:property><D:owner/></D:property>
       </D:principal>
       <D:grant>
         <D:privilege><D:read/></D:privilege>
       </D:grant>
     </D:ace>
     <D:ace>
       <D:principal>
         <D:property><D:owner/></D:property>
       </D:principal>
       <D:deny>
         <D:privilege><D:all/></D:privilege>
       </D:deny>
     </D:ace>
     <D:ace>
       <D:principal>
         <D:property><D:group/></D:property>
       </D:principal>
       <D:grant>
         <D:privilege><D:read/></D:privilege>
         <D:privilege><D:write/></D:privilege>
       </D:grant>
     </D:ace>

     <D:ace>
       <D:principal>
         <D:property><D:group/></D:property>
       </D:principal>
       <D:deny>
         <D:privilege><D:all/></D:privilege>
       </D:deny>
     </D:ace>
     <D:ace>
       <D:principal><D:all></D:principal>
       <D:grant>
         <D:privilege><D:read/></D:privilege>
       </D:grant>
     </D:ace>
   </D:acl>

   and the <acl-restrictions> would be defined as:

   <D:no-invert/>
   <D:required-principal>
     <D:all/>
     <D:property><D:owner/></D:property>
     <D:property><D:group/><D:group/>
   </D:required-principal>

   Note that the client can still get errors from a UNIX server in spite
   of obeying the <acl-restrictions>, including <D:allowed-principal>
   (adding an ACE specifying a principal other than the ones in the ACL
   above) or <D:ace-conflict> (by trying to reorder the ACEs in the
   example above), as these particular implementation semantics are too
   complex to be captured with the simple (but general) declarative
   restrictions.

7.  Access Control and existing methods

   This section defines the impact of access control functionality on
   existing methods.

7.1.  Any HTTP method

7.1.1.  Error Handling

   The WebDAV ACL mechanism requires the usage of HTTP method
   "preconditions" as described in section 1.6 of RFC3253 for ALL HTTP
   methods.  All HTTP methods have an additional precondition called
   DAV:need-privileges.  If an HTTP method fails due to insufficient
   privileges, the response body to the "403 Forbidden" error MUST
   contain the <DAV:error> element, which in turn contains the

   <DAV:need-privileges> element, which contains one or more
   <DAV:resource> elements indicating which resource had insufficient
   privileges, and what the lacking privileges were:

   <!ELEMENT need-privileges (resource)* >
   <!ELEMENT resource ( href , privilege ) >

   Since some methods require multiple permissions on multiple
   resources, this information is needed to resolve any ambiguity.
   There is no requirement that all privilege violations be reported -
   for implementation reasons, some servers may only report the first
   privilege violation.  For example:

   >> Request <<

   MOVE /a/b/ HTTP/1.1
   Host: www.example.com
   Destination: http://www.example.com/c/d

   >> Response <<

   HTTP/1.1 403 Forbidden
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <D:error xmlns:D="DAV:">
     <D:need-privileges>
       <D:resource>
         <D:href>/a</D:href>
         <D:privilege><D:unbind/></D:privilege>
       </D:resource>
       <D:resource>
         <D:href>/c</D:href>
         <D:privilege><D:bind/></D:privilege>
       </D:resource>
     </D:need-privileges>
   </D:error>

7.2.  OPTIONS

   If the server supports access control, it MUST return "access-
   control" as a field in the DAV response header from an OPTIONS
   request on any resource implemented by that server.  A value of
   "access-control" in the DAV header MUST indicate that the server
   supports all MUST level requirements and REQUIRED features specified
   in this document.

7.2.1.  Example - OPTIONS

   >> Request <<

   OPTIONS /foo.html HTTP/1.1
   Host: www.example.com
   Content-Length: 0

   >> Response <<

   HTTP/1.1 200 OK
   DAV: 1, 2, access-control
   Allow: OPTIONS, GET, PUT, PROPFIND, PROPPATCH, ACL

   In this example, the OPTIONS response indicates that the server
   supports access control and that /foo.html can have its access
   control list modified by the ACL method.

7.3.  MOVE

   When a resource is moved from one location to another due to a MOVE
   request, the non-inherited and non-protected ACEs in the DAV:acl
   property of the resource MUST NOT be modified, or the MOVE request
   fails.  Handling of inherited and protected ACEs is intentionally
   undefined to give server implementations flexibility in how they
   implement ACE inheritance and protection.

7.4.  COPY

   The DAV:acl property on the resource at the destination of a COPY
   MUST be the same as if the resource was created by an individual
   resource creation request (e.g., MKCOL, PUT).  Clients wishing to
   preserve the DAV:acl property across a copy need to read the DAV:acl
   property prior to the COPY, then perform an ACL operation on the new
   resource at the destination to restore, insofar as this is possible,
   the original access control list.

7.5.  LOCK

   A lock on a resource ensures that only the lock owner can modify ACEs
   that are not inherited and not protected  (these are the only ACEs
   that a client can modify with an ACL request).  A lock does not
   protect inherited or protected ACEs, since a client cannot modify
   them with an ACL request on that resource.

8.  Access Control Methods

8.1.  ACL

   The ACL method modifies the access control list (which can be read
   via the DAV:acl property) of a resource.  Specifically, the ACL
   method only permits modification to ACEs that are not inherited, and
   are not protected.  An ACL method invocation modifies all non-
   inherited and non-protected ACEs in a resource's access control list
   to exactly match the ACEs contained within in the DAV:acl XML element
   (specified in Section 5.5) of the request body.  An ACL request body
   MUST contain only one DAV:acl XML element.  Unless the non-inherited
   and non-protected ACEs of the DAV:acl property of the resource can be
   updated to be exactly the value specified in the ACL request, the ACL
   request MUST fail.

   It is possible that the ACEs visible to the current user in the
   DAV:acl property may only be a portion of the complete set of ACEs on
   that resource.  If this is the case, an ACL request only modifies the
   set of ACEs visible to the current user, and does not affect any
   non-visible ACE.

   In order to avoid overwriting DAV:acl changes by another client, a
   client SHOULD acquire a WebDAV lock on the resource before retrieving
   the DAV:acl property of a resource that it intends on updating.

      Implementation Note: Two common operations are to add or remove an
      ACE from an existing access control list.  To accomplish this, a
      client uses the PROPFIND method to retrieve the value of the
      DAV:acl property, then parses the returned access control list to
      remove all inherited and protected ACEs (these ACEs are tagged
      with the DAV:inherited and DAV:protected XML elements).  In the
      remaining set of non-inherited, non-protected ACEs, the client can
      add or remove one or more ACEs before submitting the final ACE set
      in the request body of the ACL method.

8.1.1.  ACL Preconditions

   An implementation MUST enforce the following constraints on an ACL
   request.  If the constraint is violated, a 403 (Forbidden) or 409
   (Conflict) response MUST be returned and the indicated XML element
   MUST be returned as a child of a top level DAV:error element in an
   XML response body.

   Though these status elements are generally expressed as empty XML
   elements (and are defined as EMPTY in the DTD), implementations MAY
   return additional descriptive XML elements as children of the status

   element.  Clients MUST be able to accept children of these status
   elements.  Clients that do not understand the additional XML elements
   should ignore them.

   (DAV:no-ace-conflict): The ACEs submitted in the ACL request MUST NOT
   conflict with each other.  This is a catchall error code indicating
   that an implementation-specific ACL restriction has been violated.

   (DAV:no-protected-ace-conflict): The ACEs submitted in the ACL
   request MUST NOT conflict with the protected ACEs on the resource.
   For example, if the resource has a protected ACE granting DAV:write
   to a given principal, then it would not be consistent if the ACL
   request submitted an ACE denying DAV:write to the same principal.

   (DAV:no-inherited-ace-conflict): The ACEs submitted in the ACL
   request MUST NOT conflict with the inherited ACEs on the resource.
   For example, if the resource inherits an ACE from its parent
   collection granting DAV:write to a given principal, then it would not
   be consistent if the ACL request submitted an ACE denying DAV:write
   to the same principal.  Note that reporting of this error will be
   implementation-dependent.  Implementations MUST either report this
   error or allow the ACE to be set, and then let normal ACE evaluation
   rules determine whether the new ACE has any impact on the privileges
   available to a specific principal.

   (DAV:limited-number-of-aces): The number of ACEs submitted in the ACL
   request MUST NOT exceed the number of ACEs allowed on that resource.
   However, ACL-compliant servers MUST support at least one ACE granting
   privileges to a single principal, and one ACE granting privileges to
   a group.

   (DAV:deny-before-grant): All non-inherited deny ACEs MUST precede all
   non-inherited grant ACEs.

   (DAV:grant-only): The ACEs submitted in the ACL request MUST NOT
   include a deny ACE.  This precondition applies only when the ACL
   restrictions of the resource include the DAV:grant-only constraint
   (defined in Section 5.6.1).

   (DAV:no-invert):  The ACL request MUST NOT include a DAV:invert
   element.  This precondition applies only when the ACL semantics of
   the resource includes the DAV:no-invert constraint (defined in
   Section 5.6.2).

   (DAV:no-abstract): The ACL request MUST NOT attempt to grant or deny
   an abstract privilege (see Section 5.3).

   (DAV:not-supported-privilege): The ACEs submitted in the ACL request
   MUST be supported by the resource.

   (DAV:missing-required-principal): The result of the ACL request MUST
   have at least one ACE for each principal identified in a
   DAV:required-principal XML element in the ACL semantics of that
   resource (see Section 5.5).

   (DAV:recognized-principal): Every principal URL in the ACL request
   MUST identify a principal resource.

   (DAV:allowed-principal): The principals specified in the ACEs
   submitted in the ACL request MUST be allowed as principals for the
   resource.  For example, a server where only authenticated principals
   can access resources would not allow the DAV:all or
   DAV:unauthenticated principals to be used in an ACE, since these
   would allow unauthenticated access to resources.

8.1.2.  Example: the ACL method

   In the following example, user "fielding", authenticated by
   information in the Authorization header, grants the principal
   identified by the URL http://www.example.com/users/esedlar (i.e., the
   user "esedlar") read and write privileges, grants the owner of the
   resource read-acl and write-acl privileges, and grants everyone read
   privileges.

   >> Request <<

   ACL /top/container/ HTTP/1.1
   Host: www.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx
   Authorization: Digest username="fielding",
     realm="users@example.com", nonce="...",
     uri="/top/container/", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:acl xmlns:D="DAV:">
     <D:ace>
       <D:principal>
         <D:href>http://www.example.com/users/esedlar</D:href>
       </D:principal>
       <D:grant>
         <D:privilege><D:read/></D:privilege>
         <D:privilege><D:write/></D:privilege>
       </D:grant>
     </D:ace>

     <D:ace>
       <D:principal>
         <D:property><D:owner/></D:property>
       </D:principal>
       <D:grant>
         <D:privilege><D:read-acl/></D:privilege>
         <D:privilege><D:write-acl/></D:privilege>
       </D:grant>
     </D:ace>
     <D:ace>
       <D:principal><D:all/></D:principal>
       <D:grant>
         <D:privilege><D:read/></D:privilege>
       </D:grant>
     </D:ace>
   </D:acl>

   >> Response <<

   HTTP/1.1 200 OK

8.1.3.  Example: ACL method failure due to protected ACE conflict

   In the following request, user "fielding", authenticated by
   information in the Authorization header, attempts to deny the
   principal identified by the URL http://www.example.com/users/esedlar
   (i.e., the user "esedlar") write privileges.  Prior to the request,
   the DAV:acl property on the resource contained a protected ACE (see
   Section 5.5.3) granting DAV:owner the DAV:read and DAV:write
   privileges.  The principal identified by URL http://www.example.com/
   users/esedlar is the owner of the resource.  The ACL method
   invocation fails because the submitted ACE conflicts with the
   protected ACE, thus violating the semantics of ACE protection.

   >> Request <<

   ACL /top/container/ HTTP/1.1
   Host: www.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx
   Authorization: Digest username="fielding",
     realm="users@example.com", nonce="...",
     uri="/top/container/", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:acl xmlns:D="DAV:">
     <D:ace>
       <D:principal>

         <D:href>http://www.example.com/users/esedlar</D:href>
       </D:principal>
       <D:deny>
         <D:privilege><D:write/></D:privilege>
       </D:deny>
     </D:ace>
   </D:acl>

   >> Response <<

   HTTP/1.1 403 Forbidden
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:error xmlns:D="DAV:">
     <D:no-protected-ace-conflict/>
   </D:error>

8.1.4.  Example: ACL method failure due to an inherited ACE conflict

   In the following request, user "ejw", authenticated by information in
   the Authorization header, tries to change the access control list on
   the resource http://www.example.com/top/index.html.  This resource
   has two inherited ACEs.

   Inherited ACE #1 grants the principal identified by URL http://
   www.example.com/users/ejw (i.e., the user "ejw") http://
   www.example.com/privs/write-all and DAV:read-acl privileges.  On this
   server, http://www.example.com/privs/write-all is an aggregate
   privilege containing DAV:write, and DAV:write-acl.

   Inherited ACE #2 grants principal DAV:all the DAV:read privilege.

   The request attempts to set a (non-inherited) ACE, denying the
   principal identified by the URL http://www.example.com/users/ejw
   (i.e., the user "ejw") DAV:write permission.  This conflicts with
   inherited ACE #1.  Note that the decision to report an inherited ACE
   conflict is specific to this server implementation.  Another server
   implementation could have allowed the new ACE to be set, and then
   used normal ACE evaluation rules to determine whether the new ACE has
   any impact on the privileges available to a principal.

   >> Request <<

   ACL /top/index.html HTTP/1.1
   Host: www.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx
   Authorization: Digest username="ejw",
     realm="users@example.com", nonce="...",
     uri="/top/index.html", response="...", opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:acl xmlns:D="DAV:" xmlns:F="http://www.example.com/privs/">
     <D:ace>
       <D:principal>
          <D:href>http://www.example.com/users/ejw</D:href>
       </D:principal>
       <D:grant><D:write/></D:grant>
     </D:ace>
   </D:acl>

   >> Response <<

   HTTP/1.1 403 Forbidden
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:error xmlns:D="DAV:">
     <D:no-inherited-ace-conflict/>
   </D:error>

8.1.5.  Example: ACL method failure due to an attempt to set grant and
        deny in a single ACE

   In this example, user "ygoland", authenticated by information in the
   Authorization header, tries to change the access control list on the
   resource http://www.example.com/diamond/engagement-ring.gif.  The ACL
   request includes a single, syntactically and semantically incorrect
   ACE, which attempts to grant the group identified by the URL http://
   www.example.com/users/friends DAV:read privilege and deny the
   principal identified by URL http://www.example.com/users/ygoland-so
   (i.e., the user "ygoland-so") DAV:read privilege.  However, it is
   illegal to have multiple principal elements, as well as both a grant
   and deny element in the same ACE, so the request fails due to poor
   syntax.

   >> Request <<

   ACL /diamond/engagement-ring.gif HTTP/1.1
   Host: www.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx
   Authorization: Digest username="ygoland",
     realm="users@example.com", nonce="...",
     uri="/diamond/engagement-ring.gif", response="...",
     opaque="..."

   <?xml version="1.0" encoding="utf-8" ?>
   <D:acl xmlns:D="DAV:">
     <D:ace>
       <D:principal>
         <D:href>http://www.example.com/users/friends</D:href>
       </D:principal>
       <D:grant><D:read/></D:grant>
       <D:principal>
         <D:href>http://www.example.com/users/ygoland-so</D:href>
       </D:principal>
       <D:deny><D:read/></D:deny>
     </D:ace>
   </D:acl>

   >> Response <<

   HTTP/1.1 400 Bad Request
   Content-Length: 0

   Note that if the request had been divided into two ACEs, one to
   grant, and one to deny, the request would have been syntactically
   well formed.

9.  Access Control Reports

9.1.  REPORT Method

   The REPORT method (defined in Section 3.6 of [RFC3253]) provides an
   extensible mechanism for obtaining information about a resource.
   Unlike the PROPFIND method, which returns the value of one or more
   named properties, the REPORT method can involve more complex
   processing.  REPORT is valuable in cases where the server has access
   to all of the information needed to perform the complex request (such
   as a query), and where it would require multiple requests for the
   client to retrieve the information needed to perform the same
   request.

   A server that supports the WebDAV Access Control Protocol MUST
   support the DAV:expand-property report (defined in Section 3.8 of
   [RFC3253]).

9.2.  DAV:acl-principal-prop-set Report

   The DAV:acl-principal-prop-set report returns, for all principals in
   the DAV:acl property (of the Request-URI) that are identified by
   http(s) URLs or by a DAV:property principal, the value of the
   properties specified in the REPORT request body.  In the case where a
   principal URL appears multiple times, the DAV:acl-principal-prop-set
   report MUST return the properties for that principal only once.
   Support for this report is REQUIRED.

   One expected use of this report is to retrieve the human readable
   name (found in the DAV:displayname property) of each principal found
   in an ACL.  This is useful for constructing user interfaces that show
   each ACE in a human readable form.

   Marshalling

      The request body MUST be a DAV:acl-principal-prop-set XML element.

      <!ELEMENT acl-principal-prop-set ANY>
      ANY value: a sequence of one or more elements, with at most one
                 DAV:prop element.
      prop: see RFC 2518, Section 12.11

      This report is only defined when the Depth header has value "0";
      other values result in a 400 (Bad Request) error response.  Note
      that [RFC3253], Section 3.6, states that if the Depth header is
      not present, it defaults to a value of "0".

      The response body for a successful request MUST be a
      DAV:multistatus XML element (i.e., the response uses the same
      format as the response for PROPFIND).  In the case where there are
      no response elements, the returned multistatus XML element is
      empty.

      multistatus: see RFC 2518, Section 12.9

      The response body for a successful DAV:acl-principal-prop-set
      REPORT request MUST contain a DAV:response element for each
      principal identified by an http(s) URL listed in a DAV:principal
      XML element of an ACE within the DAV:acl property of the resource
      identified by the Request-URI.

   Postconditions:

      (DAV:number-of-matches-within-limits): The number of matching
      principals must fall within server-specific, predefined limits.
      For example, this condition might be triggered if a search
      specification would cause the return of an extremely large number
      of responses.

9.2.1.  Example: DAV:acl-principal-prop-set Report

   Resource http://www.example.com/index.html has an ACL with three
   ACEs:

   ACE #1: All principals (DAV:all) have DAV:read and DAV:read-current-
   user-privilege-set access.

   ACE #2: The principal identified by http://www.example.com/people/
   gstein (the user "gstein") is granted DAV:write,  DAV:write-acl,
   DAV:read-acl privileges.

   ACE #3: The group identified by http://www.example.com/groups/authors
   (the "authors" group) is granted DAV:write and DAV:read-acl
   privileges.

   The following example shows a DAV:acl-principal-prop-set report
   requesting the DAV:displayname property.  It returns the value of
   DAV:displayname for resources http://www.example.com/people/gstein
   and http://www.example.com/groups/authors , but not for DAV:all,
   since this is not an http(s) URL.

   >> Request <<

   REPORT /index.html HTTP/1.1
   Host: www.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx
   Depth: 0

   <?xml version="1.0" encoding="utf-8" ?>
   <D:acl-principal-prop-set xmlns:D="DAV:">
     <D:prop>
       <D:displayname/>
     </D:prop>
   </D:acl-principal-prop-set>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.example.com/people/gstein</D:href>
       <D:propstat>
         <D:prop>
           <D:displayname>Greg Stein</D:displayname>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>http://www.example.com/groups/authors</D:href>
       <D:propstat>
         <D:prop>
           <D:displayname>Site authors</D:displayname>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

9.3.  DAV:principal-match REPORT

   The DAV:principal-match REPORT is used to identify all members (at
   any depth) of the collection identified by the Request-URI that are
   principals and that match the current user.  In particular, if the
   collection contains principals, the report can be used to identify
   all members of the collection that match the current user.
   Alternatively, if the collection contains resources that have a
   property that identifies a principal (e.g., DAV:owner), the report
   can be used to identify all members of the collection whose property
   identifies a principal that matches the current user.  For example,
   this report can return all of the resources in a collection hierarchy
   that are owned by the current user.  Support for this report is
   REQUIRED.

   Marshalling:

      The request body MUST be a DAV:principal-match XML element.
      <!ELEMENT principal-match ((principal-property | self), prop?)>
      <!ELEMENT principal-property ANY>

      ANY value: an element whose value identifies a property.  The
      expectation is the value of the named property typically contains
      an href element that contains the URI of a principal
      <!ELEMENT self EMPTY>
      prop: see RFC 2518, Section 12.11

      This report is only defined when the Depth header has value "0";
      other values result in a 400 (Bad Request) error response.  Note
      that [RFC3253], Section 3.6, states that if the Depth header is
      not present, it defaults to a value of "0".  The response body for
      a successful request MUST be a DAV:multistatus XML element.  In
      the case where there are no response elements, the returned
      multistatus XML element is empty.

      multistatus: see RFC 2518, Section 12.9

      The response body for a successful DAV:principal-match REPORT
      request MUST contain a DAV:response element for each member of the
      collection that matches the current user.  When the
      DAV:principal-property element is used, a match occurs if the
      current user is matched by the principal identified by the URI
      found in the DAV:href element of the property identified by the
      DAV:principal-property element.  When the DAV:self element is used
      in a DAV:principal-match report issued against a group, it matches
      the group if a member identifies the same principal as the current
      user.

      If DAV:prop is specified in the request body, the properties
      specified in the DAV:prop element MUST be reported in the
      DAV:response elements.

9.3.1.  Example: DAV:principal-match REPORT

   The following example identifies the members of the collection
   identified by the URL http://www.example.com/doc that are owned by
   the current user.  The current user ("gclemm") is authenticated using
   Digest authentication.

   >> Request <<

   REPORT /doc/ HTTP/1.1
   Host: www.example.com
   Authorization: Digest username="gclemm",
     realm="users@example.com", nonce="...",
     uri="/papers/", response="...", opaque="..."
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx
   Depth: 0

   <?xml version="1.0" encoding="utf-8" ?>
   <D:principal-match xmlns:D="DAV:">
     <D:principal-property>
       <D:owner/>
     </D:principal-property>
   </D:principal-match>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.example.com/doc/foo.html</D:href>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:response>
     <D:response>
       <D:href>http://www.example.com/doc/img/bar.gif</D:href>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:response>
   </D:multistatus>

9.4.  DAV:principal-property-search REPORT

   The DAV:principal-property-search REPORT performs a search for all
   principals whose properties contain character data that matches the
   search criteria specified in the request.  One expected use of this
   report is to discover the URL of a principal associated with a given
   person or group by searching for them by name.  This is done by
   searching over DAV:displayname, which is defined on all principals.

   The actual search method (exact matching vs. substring matching vs,
   prefix-matching, case-sensitivity) deliberately is left to the server
   implementation to allow implementation on a wide set of possible user
   management systems.  In cases where the implementation of
   DAV:principal-property-search is not constrained by the semantics of
   an underlying user management repository, preferred default semantics
   are caseless substring matches.

   For implementation efficiency, servers do not typically support
   searching on all properties.  A search requesting properties that are
   not searchable for a particular principal will not match that
   principal.

   Support for the DAV:principal-property-search report is REQUIRED.

      Implementation Note: The value of a WebDAV property is a sequence
      of well-formed XML, and hence can include any character in the
      Unicode/ISO-10646 standard, that is, most known characters in
      human languages.  Due to the idiosyncrasies of case mapping across
      human languages, implementation of case-insensitive matching is
      non-trivial.  Implementors of servers that do perform substring
      matching are strongly encouraged to consult "The Unicode Standard"
      [UNICODE4], especially Section 5.18, Subsection "Caseless
      Matching", for guidance when implementing their case-insensitive
      matching algorithms.

      Implementation Note: Some implementations of this protocol will
      use an LDAP repository for storage of principal metadata.  The
      schema describing each attribute (akin to a WebDAV property) in an
      LDAP repository specifies whether it supports case-sensitive or
      caseless searching.  One of the benefits of leaving the search
      method to the discretion of the server implementation is the
      default LDAP attribute search behavior can be used when
      implementing the DAV:principal-property-search report.

   Marshalling:

      The request body MUST be a DAV:principal-property-search XML
      element containing a search specification and an optional list of
      properties.  For every principal that matches the search
      specification, the response will contain the value of the
      requested properties on that principal.

      <!ELEMENT principal-property-search
       ((property-search+), prop?, apply-to-principal-collection-set?) >

      By default, the report searches all members (at any depth) of the
      collection identified by the Request-URI.  If DAV:apply-to-
      principal-collection-set is specified in the request body, the
      request is applied instead to each collection identified by the
      DAV:principal-collection-set property of the resource identified
      by the Request-URI.

      The DAV:property-search element contains a prop element
      enumerating the properties to be searched and a match element,
      containing the search string.

      <!ELEMENT property-search (prop, match) >
      prop: see RFC 2518, Section 12.11

      <!ELEMENT match #PCDATA >

      Multiple property-search elements or multiple elements within a
      DAV:prop element will be interpreted with a logical AND.

      This report is only defined when the Depth header has value "0";
      other values result in a 400 (Bad Request) error response.  Note
      that [RFC3253], Section 3.6, states that if the Depth header is
      not present, it defaults to a value of "0".

      The response body for a successful request MUST be a
      DAV:multistatus XML element.  In the case where there are no
      response elements, the returned multistatus XML element is empty.

      multistatus: see RFC 2518, Section 12.9

      The response body for a successful DAV:principal-property-search
      REPORT request MUST contain  a DAV:response element for each
      principal whose property values satisfy the search specification
      given in DAV:principal-property-search.

      If DAV:prop is specified in the request body, the properties
      specified in the DAV:prop element MUST be reported in the
      DAV:response elements.

   Preconditions:

      None

   Postconditions:

      (DAV:number-of-matches-within-limits): The number of matching
      principals must fall within server-specific, predefined limits.
      For example, this condition might be triggered if a search
      specification would cause the return of an extremely large number
      of responses.

9.4.1.  Matching

   There are several cases to consider when matching strings.  The
   easiest case is when a property value is "simple" and has only
   character information item content (see [REC-XML-INFOSET]).  For
   example, the search string "julian" would match the DAV:displayname
   property with value "Julian Reschke".  Note that the on-the-wire
   marshaling of DAV:displayname in this case is:

   <D:displayname xmlns:D="DAV:">Julian Reschke</D:displayname>

   The name of the property is encoded into the XML element information
   item, and the character information item content of the property is
   "Julian Reschke".

   A more complicated case occurs when properties have mixed content
   (that is, compound values consisting of multiple child element items,
   other types of information items, and character information item
   content).  Consider the property "aprop" in the namespace "http://
   www.example.com/props/", marshaled as:

   <W:aprop xmlns:W="http://www.example.com/props/">
     {cdata 0}<W:elem1>{cdata 1}</W:elem1>
     <W:elem2>{cdata 2}</W:elem2>{cdata 3}
   </W:aprop>

   In this case, matching is performed on each individual contiguous
   sequence of character information items.  In the example above, a
   search string would be compared to the four following strings:

   {cdata 0}
   {cdata 1}
   {cdata 2}
   {cdata 3}

   That is, four individual matches would be performed, one each for
   {cdata 0}, {cdata 1}, {cdata 2}, and {cdata 3}.

9.4.2.  Example: successful DAV:principal-property-search REPORT

   In this example, the client requests the principal URLs of all users
   whose DAV:displayname property contains the substring "doE" and whose
   "title" property in the namespace "http://BigCorp.com/ns/" (that is,
   their professional title) contains "Sales".  In addition, the client
   requests five properties to be returned with the matching principals:

   In the DAV: namespace: displayname

   In the http://www.example.com/ns/ namespace: department, phone,
   office, salary

   The response shows that two principal resources meet the search
   specification, "John Doe" and "Zygdoebert Smith".  The property
   "salary" in namespace "http://www.example.com/ns/" is not returned,
   since the principal making the request does not have sufficient
   access permissions to read this property.

   >> Request <<

   REPORT /users/ HTTP/1.1
   Host: www.example.com
   Content-Type: text/xml; charset=utf-8
   Content-Length: xxxx
   Depth: 0

   <?xml version="1.0" encoding="utf-8" ?>
   <D:principal-property-search xmlns:D="DAV:">
     <D:property-search>
       <D:prop>
         <D:displayname/>
       </D:prop>
       <D:match>doE</D:match>
     </D:property-search>
     <D:property-search>
       <D:prop xmlns:B="http://www.example.com/ns/">
         <B:title/>
       </D:prop>
       <D:match>Sales</D:match>
     </D:property-search>
     <D:prop xmlns:B="http://www.example.com/ns/">
       <D:displayname/>
       <B:department/>
       <B:phone/>
       <B:office/>
       <B:salary/>
     </D:prop>
   </D:principal-property-search>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset=utf-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:" xmlns:B="http://BigCorp.com/ns/">
     <D:response>
       <D:href>http://www.example.com/users/jdoe</D:href>
       <D:propstat>

         <D:prop>
           <D:displayname>John Doe</D:displayname>
           <B:department>Widget Sales</B:department>
           <B:phone>234-4567</B:phone>
           <B:office>209</B:office>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <D:propstat>
         <D:prop>
           <B:salary/>
         </D:prop>
         <D:status>HTTP/1.1 403 Forbidden</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>http://www.example.com/users/zsmith</D:href>
       <D:propstat>
         <D:prop>
           <D:displayname>Zygdoebert Smith</D:displayname>
           <B:department>Gadget Sales</B:department>
           <B:phone>234-7654</B:phone>
           <B:office>114</B:office>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <D:propstat>
         <D:prop>
           <B:salary/>
         </D:prop>
         <D:status>HTTP/1.1 403 Forbidden</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

9.5.  DAV:principal-search-property-set REPORT

   The DAV:principal-search-property-set REPORT identifies those
   properties that may be searched using the DAV:principal-property-
   search REPORT (defined in Section 9.4).

   Servers MUST support the DAV:principal-search-property-set REPORT on
   all collections identified in the value of a DAV:principal-
   collection-set property.

   An access control protocol user agent could use the results of the
   DAV:principal-search-property-set REPORT to present a query interface
   to the user for retrieving principals.

   Support for this report is REQUIRED.

      Implementation Note: Some clients will have only limited screen
      real estate for the display of lists of searchable properties.  In
      this case, a user might appreciate having the most frequently
      searched properties be displayed on-screen, rather than having to
      scroll through a long list of searchable properties.  One
      mechanism for signaling the most frequently searched properties is
      to return them towards the start of a list of properties.  A
      client can then preferentially display the list of properties in
      order, increasing the likelihood that the most frequently searched
      properties will appear on-screen, and will not require scrolling
      for their selection.

   Marshalling:

      The request body MUST be an empty DAV:principal-search-property-
      set XML element.

      This report is only defined when the Depth header has value "0";
      other values result in a 400 (Bad Request) error response.  Note
      that [RFC3253], Section 3.6, states that if the Depth header is
      not present, it defaults to a value of "0".

      The response body MUST be  a DAV:principal-search-property-set XML
      element, containing a DAV:principal-search-property XML element
      for each property that may be searched with the DAV:principal-
      property-search REPORT.  A server MAY limit its response to just a
      subset of the searchable properties, such as those likely to be
      useful to an interactive access control client.

      <!ELEMENT principal-search-property-set
       (principal-search-property*) >

      Each DAV:principal-search-property XML element contains exactly
      one searchable property, and a description of the property.

      <!ELEMENT principal-search-property (prop, description) >

      The DAV:prop element contains one principal property on which the
      server is able to perform a DAV:principal-property-search REPORT.

      prop: see RFC 2518, Section 12.11

      The description element is a human-readable description of what
      information this property represents.  Servers MUST indicate the
      human language of the description using the xml:lang attribute and
      SHOULD consider the HTTP Accept-Language request header when
      selecting one of multiple available languages.

      <!ELEMENT description #PCDATA >

9.5.1.  Example: DAV:principal-search-property-set REPORT

   In this example, the client determines the set of searchable
   principal properties by requesting the DAV:principal-search-
   property-set REPORT on the root of the server's principal URL
   collection set, identified by http://www.example.com/users/.

   >> Request <<

   REPORT /users/ HTTP/1.1
   Host: www.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx
   Accept-Language: en, de
   Authorization: BASIC d2FubmFtYWs6cGFzc3dvcmQ=
   Depth: 0

   <?xml version="1.0" encoding="utf-8" ?>
   <D:principal-search-property-set xmlns:D="DAV:"/>

   >> Response <<

   HTTP/1.1 200 OK
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:principal-search-property-set xmlns:D="DAV:">
     <D:principal-search-property>
       <D:prop>
         <D:displayname/>
       </D:prop>
       <D:description xml:lang="en">Full name</D:description>
     </D:principal-search-property>
     <D:principal-search-property>
       <D:prop xmlns:B="http://BigCorp.com/ns/">
         <B:title/>

       </D:prop>
       <D:description xml:lang="en">Job title</D:description>
     </D:principal-search-property>
   </D:principal-search-property-set>

10.  XML Processing

   Implementations of this specification MUST support the XML element
   ignore rule, as specified in Section 23.3.2 of [RFC2518], and the XML
   Namespace recommendation [REC-XML-NAMES].

   Note that use of the DAV namespace is reserved for XML elements and
   property names defined in a standards-track or Experimental IETF RFC.

11.  Internationalization Considerations

   In this specification, the only human-readable content can be found
   in the description XML element, found within the DAV:supported-
   privilege-set property.  This element contains a human-readable
   description of the capabilities controlled by a privilege.  As a
   result, the description element must be capable of representing
   descriptions in multiple character sets.  Since the description
   element is found within a WebDAV property, it is represented on the
   wire as XML [REC-XML], and hence can leverage XML's language tagging
   and character set encoding capabilities.  Specifically, XML
   processors at minimum must be able to read XML elements encoded using
   the UTF-8 [RFC3629] encoding of the ISO 10646 multilingual plane.
   XML examples in this specification demonstrate use of the charset
   parameter of the Content-Type header, as defined in [RFC3023], as
   well as the XML "encoding" attribute, which together provide charset
   identification information for MIME and XML processors.  Furthermore,
   this specification requires server implementations to tag description
   fields with the xml:lang attribute (see Section 2.12 of [REC-XML]),
   which specifies the human language of the description.  Additionally,
   server implementations should take into account the value of the
   Accept-Language HTTP header to determine which description string to
   return.

   For XML elements other than the description element, it is expected
   that implementations will treat the property names, privilege names,
   and values as tokens, and convert these tokens into human-readable
   text in the user's language and character set when displayed to a
   person.  Only a generic WebDAV property display utility would display
   these values in their raw form to a human user.

   For error reporting, we follow the convention of HTTP/1.1 status
   codes, including with each status code a short, English description
   of the code (e.g., 200 (OK)).  While the possibility exists that a

   poorly crafted user agent would display this message to a user,
   internationalized applications will ignore this message, and display
   an appropriate message in the user's language and character set.

   Further internationalization considerations for this protocol are
   described in the WebDAV Distributed Authoring protocol specification
   [RFC2518].

12.  Security Considerations

   Applications and users of this access control protocol should be
   aware of several security considerations, detailed below.  In
   addition to the discussion in this document, the security
   considerations detailed in the HTTP/1.1 specification [RFC2616], the
   WebDAV Distributed Authoring Protocol specification [RFC2518], and
   the XML Media Types specification [RFC3023] should be considered in a
   security analysis of this protocol.

12.1.  Increased Risk of Compromised Users

   In the absence of a mechanism for remotely manipulating access
   control lists, if a single user's authentication credentials are
   compromised, only those resources for which the user has access
   permission can be read, modified, moved, or deleted.  With the
   introduction of this access control protocol, if a single compromised
   user has the ability to change ACLs for a broad range of other users
   (e.g., a super-user), the number of resources that could be altered
   by a single compromised user increases.  This risk can be mitigated
   by limiting the number of people who have write-acl privileges across
   a broad range of resources.

12.2.  Risks of the DAV:read-acl and DAV:current-user-privilege-set
       Privileges

   The ability to read the access privileges (stored in the DAV:acl
   property), or the privileges permitted the currently authenticated
   user (stored in the DAV:current-user-privilege-set property) on a
   resource may seem innocuous, since reading an ACL cannot possibly
   affect the resource's state.  However, if all resources have world-
   readable ACLs, it is possible to perform an exhaustive search for
   those resources that have inadvertently left themselves in a
   vulnerable state, such as being world-writable.  In particular, the
   property retrieval method PROPFIND, executed with Depth infinity on
   an entire hierarchy, is a very efficient way to retrieve the DAV:acl
   or DAV:current-user-privilege-set properties.  Once found, this
   vulnerability can be exploited by a denial of service attack in which
   the open resource is repeatedly overwritten.  Alternately, writable
   resources can be modified in undesirable ways.

   To reduce this risk, read-acl privileges should not be granted to
   unauthenticated principals, and restrictions on read-acl and read-
   current-user-privilege-set privileges for authenticated principals
   should be carefully analyzed when deploying this protocol.  Access to
   the current-user-privilege-set property will involve a tradeoff of
   usability versus security.  When the current-user-privilege-set is
   visible, user interfaces are expected to provide enhanced information
   concerning permitted and restricted operations, yet this information
   may also indicate a vulnerability that could be exploited.
   Deployment of this protocol will need to evaluate this tradeoff in
   light of the requirements of the deployment environment.

12.3.  No Foreknowledge of Initial ACL

   In an effort to reduce protocol complexity, this protocol
   specification intentionally does not address the issue of how to
   manage or discover the initial ACL that is placed upon a resource
   when it is created.  The only way to discover the initial ACL is to
   create a new resource, then retrieve the value of the DAV:acl
   property.  This assumes the principal creating the resource also has
   been granted the DAV:read-acl privilege.

   As a result, it is possible that a principal could create a resource,
   and then discover that its ACL grants privileges that are
   undesirable.  Furthermore, this protocol makes it possible (though
   unlikely) that the creating principal could be unable to modify the
   ACL, or even delete the resource.  Even when the ACL can be modified,
   there will be a short period of time when the resource exists with
   the initial ACL before its new ACL can be set.

   Several factors mitigate this risk.  Human principals are often aware
   of the default access permissions in their editing environments and
   take this into account when writing information.  Furthermore,
   default privilege policies are usually very conservative, limiting
   the privileges granted by the initial ACL.

13.  Authentication

   Authentication mechanisms defined for use with HTTP and WebDAV also
   apply to this WebDAV Access Control Protocol, in particular the Basic
   and Digest authentication mechanisms defined in [RFC2617].
   Implementation of the ACL spec requires that Basic authentication, if
   used, MUST only be supported over secure transport such as TLS.

14.  IANA Considerations

   This document uses the namespace defined by [RFC2518] for XML
   elements.  That is, this specification uses the "DAV:" URI namespace,
   previously registered in the URI schemes registry.  All other IANA
   considerations mentioned in [RFC2518] are also applicable to this
   specification.

15.  Acknowledgements

   This protocol is the collaborative product of the WebDAV ACL design
   team: Bernard Chester, Geoff Clemm, Anne Hopkins, Barry Lind, Sean
   Lyndersay, Eric Sedlar, Greg Stein, and Jim Whitehead.  The authors
   are grateful for the detailed review and comments provided by Jim
   Amsden, Dylan Barrell, Gino Basso, Murthy Chintalapati, Lisa
   Dusseault, Stefan Eissing, Tim Ellison, Yaron Goland, Dennis
   Hamilton, Laurie Harper, Eckehard Hermann, Ron Jacobs, Chris Knight,
   Remy Maucherat, Larry Masinter, Joe Orton, Peter Raymond, and Keith
   Wannamaker.  We thank Keith Wannamaker for the initial text of the
   principal property search sections.  Prior work on WebDAV access
   control protocols has been performed by Yaron Goland, Paul Leach,
   Lisa Dusseault, Howard Palmer, and Jon Radoff.  We would like to
   acknowledge the foundation laid for us by the authors of the DeltaV,
   WebDAV and HTTP protocols upon which this protocol is layered, and
   the invaluable feedback from the WebDAV working group.

16.  References

16.1.  Normative References

   [REC-XML]         Bray, T., Paoli, J., Sperberg-McQueen, C. and E.
                     Maler, "Extensible Markup Language (XML) 1.0
                     ((Third ed)", W3C REC REC-xml-20040204, February
                     2004, <http://www.w3.org/TR/2004/REC-xml-20040204>.

   [REC-XML-INFOSET] Cowan, J. and R. Tobin, "XML Information Set
                     (Second Edition)", W3C REC REC-xml-infoset-
                     20040204, February 2004,
                     <http://www.w3.org/TR/2004/REC-xml-infoset-
                     20040204/>.

   [REC-XML-NAMES]   Bray, T., Hollander, D. and A. Layman, "Namespaces
                     in XML", W3C REC REC-xml-names-19990114, January
                     1999, <http://www.w3.org/TR/1999/REC-xml-names-
                     19990114>.

   [RFC2119]         Bradner, S., "Key words for use in RFCs to Indicate
                     Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2518]         Goland, Y., Whitehead, E., Faizi, A., Carter, S.
                     and D. Jensen, "HTTP Extensions for Distributed
                     Authoring -- WEBDAV", RFC 2518, February 1999.

   [RFC2616]         Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
                     Masinter, L., Leach, P. and T. Berners-Lee,
                     "Hypertext Transfer Protocol -- HTTP/1.1", RFC
                     2616, June 1999.

   [RFC2617]         Franks, J., Hallam-Baker, P., Hostetler, J.,
                     Lawrence, S., Leach, P., Luotonen, A. and L.
                     Stewart, "HTTP Authentication: Basic and Digest
                     Access Authentication", RFC 2617, June 1999.

   [RFC3023]         Murata, M., St.Laurent, S. and D. Kohn, "XML Media
                     Types", RFC 3023, January 2001.

   [RFC3253]         Clemm, G., Amsden, J., Ellison, T., Kaler, C. and
                     J. Whitehead, "Versioning Extensions to WebDAV",
                     RFC 3253, March 2002.

   [RFC3530]         Shepler, S., Ed., Callaghan, B., Robinson, D.,
                     Thurlow, R., Beame, C., Eisler, M. and D. Noveck,
                     "Network File System (NFS) version 4 Protocol", RFC
                     3530, April 2003.

   [RFC3629]         Yergeau, F., "UTF-8, a transformation format of ISO
                     10646", STD 63, RFC 3629 November 2003.

16.2.  Informative References

   [RFC2251]         Wahl, M., Howes, T. and S. Kille, "Lightweight
                     Directory Access Protocol (v3)", RFC 2251, December
                     1997.

   [RFC2255]         Howes, T. and M. Smith, "The LDAP URL Format", RFC
                     2255, December 1997.

   [UNICODE4]        The Unicode Consortium, "The Unicode Standard -
                     Version 4.0", Addison-Wesley , August 2003,
                     <http://www.unicode.org/versions/Unicode4.0.0/>.
                     ISBN 0321185781.

Appendix A. WebDAV XML Document Type Definition Addendum

   All XML elements defined in this Document Type Definition (DTD)
   belong to the DAV namespace. This DTD should be viewed as an addendum
   to the DTD provided in [RFC2518], section 23.1.

   <!-- Privileges -- (Section 3)>

   <!ELEMENT read EMPTY>
   <!ELEMENT write EMPTY>
   <!ELEMENT write-properties EMPTY>
   <!ELEMENT write-content EMPTY>
   <!ELEMENT unlock EMPTY>
   <!ELEMENT read-acl EMPTY>
   <!ELEMENT read-current-user-privilege-set EMPTY>
   <!ELEMENT write-acl EMPTY>
   <!ELEMENT bind EMPTY>
   <!ELEMENT unbind EMPTY>
   <!ELEMENT all EMPTY>

   <!-- Principal Properties (Section 4) -->

   <!ELEMENT principal EMPTY>

   <!ELEMENT alternate-URI-set (href*)>
   <!ELEMENT principal-URL (href)>
   <!ELEMENT group-member-set (href*)>
   <!ELEMENT group-membership (href*)>

   <!-- Access Control Properties (Section 5) -->

   <!-- DAV:owner Property (Section 5.1) -->

   <!ELEMENT owner (href?)>

   <!-- DAV:group Property (Section 5.2) -->

   <!ELEMENT group (href?)>

   <!-- DAV:supported-privilege-set Property (Section 5.3) -->

   <!ELEMENT supported-privilege-set (supported-privilege*)>
   <!ELEMENT supported-privilege
    (privilege, abstract?, description, supported-privilege*)>

   <!ELEMENT privilege ANY>
   <!ELEMENT abstract EMPTY>
   <!ELEMENT description #PCDATA>

   <!-- DAV:current-user-privilege-set Property (Section 5.4) -->

   <!ELEMENT current-user-privilege-set (privilege*)>

   <!-- DAV:acl Property (Section 5.5) -->

   <!ELEMENT acl (ace)* >
   <!ELEMENT ace ((principal | invert), (grant|deny), protected?,
    inherited?)>

   <!ELEMENT principal (href)
    | all | authenticated | unauthenticated
    | property | self)>

   <!ELEMENT all EMPTY>
   <!ELEMENT authenticated EMPTY>
   <!ELEMENT unauthenticated EMPTY>
   <!ELEMENT property ANY>
   <!ELEMENT self EMPTY>

   <!ELEMENT invert principal>

   <!ELEMENT grant (privilege+)>
   <!ELEMENT deny (privilege+)>
   <!ELEMENT privilege ANY>

   <!ELEMENT protected EMPTY>

   <!ELEMENT inherited (href)>

   <!-- DAV:acl-restrictions Property (Section 5.6) -->

   <!ELEMENT acl-restrictions (grant-only?, no-invert?,
    deny-before-grant?, required-principal?)>

   <!ELEMENT grant-only EMPTY>
   <!ELEMENT no-invert EMPTY>
   <!ELEMENT deny-before-grant EMPTY>

   <!ELEMENT required-principal
    (all? | authenticated? | unauthenticated? | self? | href*
    |property*)>

   <!-- DAV:inherited-acl-set Property (Section 5.7) -->

   <!ELEMENT inherited-acl-set (href*)>

   <!-- DAV:principal-collection-set Property (Section 5.8) -->

   <!ELEMENT principal-collection-set (href*)>

   <!-- Access Control and Existing Methods (Section 7) -->

   <!ELEMENT need-privileges (resource)* >
   <!ELEMENT resource ( href, privilege )

   <!-- ACL method preconditions (Section 8.1.1) -->

   <!ELEMENT no-ace-conflict EMPTY>
   <!ELEMENT no-protected-ace-conflict EMPTY>
   <!ELEMENT no-inherited-ace-conflict EMPTY>
   <!ELEMENT limited-number-of-aces EMPTY>
   <!ELEMENT grant-only EMPTY>
   <!ELEMENT no-invert EMPTY>
   <!ELEMENT deny-before-grant EMPTY>
   <!ELEMENT no-abstract EMPTY>
   <!ELEMENT not-supported-privilege EMPTY>
   <!ELEMENT missing-required-principal EMPTY>
   <!ELEMENT recognized-principal EMPTY>
   <!ELEMENT allowed-principal EMPTY>

   <!-- REPORTs (Section 9) -->

   <!ELEMENT acl-principal-prop-set ANY>
   ANY value: a sequence of one or more elements, with at most one
   DAV:prop element.

   <!ELEMENT principal-match ((principal-property | self), prop?)>
   <!ELEMENT principal-property ANY>
   ANY value: an element whose value identifies a property. The
   expectation is the value of the named property typically contains
   an href element that contains the URI of a principal
   <!ELEMENT self EMPTY>

   <!ELEMENT principal-property-search ((property-search+), prop?) >
   <!ELEMENT property-search (prop, match) >
   <!ELEMENT match #PCDATA >

   <!ELEMENT principal-search-property-set (
    principal-search-property*) >
   <!ELEMENT principal-search-property (prop, description) >
   <!ELEMENT description #PCDATA >

Appendix B. WebDAV Method Privilege Table (Normative)

   The following table of WebDAV methods (as defined in RFC 2518, 2616,
   and 3253) clarifies which privileges are required for access for each
   method.  Note that the privileges listed, if denied, MUST cause
   access to be denied.  However, given that a specific implementation
   MAY define an additional custom privilege to control access to
   existing methods, having all of the indicated privileges does not
   mean that access will be granted.  Note that lack of the indicated
   privileges does not imply that access will be denied, since a
   particular implementation may use a sub-privilege aggregated under
   the indicated privilege to control access.  Privileges required refer
   to the current resource being processed unless otherwise specified.

   +---------------------------------+---------------------------------+
   | METHOD                          | PRIVILEGES                      |
   +---------------------------------+---------------------------------+
   | GET                             | <D:read>                        |
   | HEAD                            | <D:read>                        |
   | OPTIONS                         | <D:read>                        |
   | PUT (target exists)             | <D:write-content> on target     |
   |                                 | resource                        |
   | PUT (no target exists)          | <D:bind> on parent collection   |
   |                                 | of target                       |
   | PROPPATCH                       | <D:write-properties>            |
   | ACL                             | <D:write-acl>                   |
   | PROPFIND                        | <D:read> (plus <D:read-acl> and |
   |                                 | <D:read-current-user-privilege- |
   |                                 | set> as needed)                 |
   | COPY (target exists)            | <D:read>, <D:write-content> and |
   |                                 | <D:write-properties> on target  |
   |                                 | resource                        |
   | COPY (no target exists)         | <D:read>, <D:bind> on target    |
   |                                 | collection                      |
   | MOVE (no target exists)         | <D:unbind> on source collection |
   |                                 | and <D:bind> on target          |
   |                                 | collection                      |
   | MOVE (target exists)            | As above, plus <D:unbind> on    |
   |                                 | the target collection           |
   | DELETE                          | <D:unbind> on parent collection |
   | LOCK (target exists)            | <D:write-content>               |
   | LOCK (no target exists)         | <D:bind> on parent collection   |
   | MKCOL                           | <D:bind> on parent collection   |
   | UNLOCK                          | <D:unlock>                      |
   | CHECKOUT                        | <D:write-properties>            |
   | CHECKIN                         | <D:write-properties>            |
   | REPORT                          | <D:read> (on all referenced     |
   |                                 | resources)                      |
   | VERSION-CONTROL                 | <D:write-properties>            |
   | MERGE                           | <D:write-content>               |
   | MKWORKSPACE                     | <D:write-content> on parent     |
   |                                 | collection                      |
   | BASELINE-CONTROL                | <D:write-properties> and        |
   |                                 | <D:write-content>               |
   | MKACTIVITY                      | <D:write-content> on parent     |
   |                                 | collection                      |
   +---------------------------------+---------------------------------+

Index

   A
      ACL method  40

   C
      Condition Names
         DAV:allowed-principal (pre)  42
         DAV:deny-before-grant (pre)  41
         DAV:grant-only (pre)  41
         DAV:limited-number-of-aces (pre)  41
         DAV:missing-required-principal (pre)  42
         DAV:no-abstract (pre)  41
         DAV:no-ace-conflict (pre)  41
         DAV:no-inherited-ace-conflict (pre)  41
         DAV:no-invert (pre)  41
         DAV:no-protected-ace-conflict (pre)  41
         DAV:not-supported-privilege (pre)  42
         DAV:number-of-matches-within-limits (post)  48, 53
         DAV:recognized-principal (pre)  42

   D
      DAV header
         compliance class 'access-control'  38
      DAV:acl property  23
      DAV:acl-principal-prop-set report  48
      DAV:acl-restrictions property  27
      DAV:all privilege  13
      DAV:allowed-principal precondition  42
      DAV:alternate-URI-set property  14
      DAV:bind privilege  12
      DAV:current-user-privilege-set property  21
      DAV:deny-before-grant precondition  41
      DAV:grant-only precondition  41
      DAV:group property  18
      DAV:group-member-set property  14
      DAV:group-membership property  14
      DAV:inherited-acl-set property  29
      DAV:limited-number-of-aces precondition  41
      DAV:missing-required-principal precondition  42
      DAV:no-abstract precondition  41
      DAV:no-ace-conflict precondition  41
      DAV:no-inherited-ace-conflict precondition  41
      DAV:no-invert precondition  41
      DAV:no-protected-ace-conflict precondition  41
      DAV:not-supported-privilege precondition  42
      DAV:number-of-matches-within-limits postcondition  48, 53
      DAV:owner property  15

      DAV:principal resource type  13
      DAV:principal-collection-set property  30
      DAV:principal-match report  50
      DAV:principal-property-search  51
      DAV:principal-search-property-set  56
      DAV:principal-URL property  14
      DAV:read privilege  10
      DAV:read-acl privilege  11
      DAV:read-current-user-privilege-set privilege  12
      DAV:recognized-principal precondition  42
      DAV:supported-privilege-set property  18
      DAV:unbind privilege  12
      DAV:unlock privilege  11
      DAV:write privilege  10
      DAV:write-acl privilege  12
      DAV:write-content privilege  10
      DAV:write-properties privilege  10

   M
      Methods
         ACL  40

   P
      Privileges
         DAV:all  13
         DAV:bind  12
         DAV:read  10
         DAV:read-acl  11
         DAV:read-current-user-privilege-set  12
         DAV:unbind  12
         DAV:unlock  11
         DAV:write  10
         DAV:write-acl  12
         DAV:write-content  11
         DAV:write-properties  10
      Properties
         DAV:acl  23
         DAV:acl-restrictions  27
         DAV:alternate-URI-set  14
         DAV:current-user-privilege-set  21
         DAV:group  18
         DAV:group-member-set  14
         DAV:group-membership  14
         DAV:inherited-acl-set  29
         DAV:owner  15
         DAV:principal-collection-set  30
         DAV:principal-URL  14
         DAV:supported-privilege-set  18

   R
      Reports
         DAV:acl-principal-prop-set  47
         DAV:principal-match  49
         DAV:principal-property-search  51
         DAV:principal-search-property-set  56
      Resource Types
         DAV:principal  13

Authors' Addresses

   Geoffrey Clemm
   IBM
   20 Maguire Road
   Lexington, MA  02421

   EMail: geoffrey.clemm@us.ibm.com

   Julian F. Reschke
   greenbytes GmbH
   Salzmannstrasse 152
   Muenster, NW  48159
   Germany

   EMail: julian.reschke@greenbytes.de

   Eric Sedlar
   Oracle Corporation
   500 Oracle Parkway
   Redwood Shores, CA  94065

   EMail: eric.sedlar@oracle.com

   Jim Whitehead
   U.C. Santa Cruz, Dept. of Computer Science
   1156 High Street
   Santa Cruz, CA  95064

   EMail: ejw@cse.ucsc.edu

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