INTERNET-DRAFT                 Geoffrey Clemm, IBM
  draft-ietf-webdav-acl-10
    draft-ietf-webdav-acl-11       Anne Hopkins, Microsoft Corporation Corporatio
				   Eric Sedlar, Oracle Corporation
				   Jim Whitehead, U.C. Santa Cruz

    Expires September 15, 2003 March 15, 10, 2004         September 10, 2003

			WebDAV Access Control Protocol

    Status of this Memo
    This document is an Internet-Draft and is subject to all provisions of
    Section 10 of RFC2026.
    Internet-Drafts are working documents of the Internet Engineering Task
    Force (IETF), its areas, and its working groups. Note that other groups
    may also distribute working documents as Internet-Drafts.
    Internet-Drafts are draft documents valid for a maximum of six months
    and may be updated, replaced, or obsoleted by other documents at any
    time. It is inappropriate to use Internet- Drafts Internet-Drafts as reference material
    or to cite them other than as "work in progress."
    The list of current Internet-Drafts can be accessed at
    http://www.ietf.org/ietf/1id-abstracts.txt
    The list of Internet-Draft Shadow Directories can be accessed at
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    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.
    This document is a product of the Web Distributed Authoring and
    Versioning (WebDAV) working group of the Internet Engineering Task
    Force. Comments on this draft are welcomed, and should be addressed to
    the acl@webdav.org mailing list. Other related documents can be found
    at http://www.example.com/acl/, and
    http://www.ics.uci.edu/pub/ietf/webdav/.

    Clemm, et al. Hopkins, Sedlar, Whitehead
			      [Page 1] 
    Table of Contents

  WEBDAV ACCESS CONTROL PROTOCOL............................1

  STATUS OF THIS MEMO.......................................1

  ABSTRACT..................................................1

  TABLE OF CONTENTS.........................................2

    1 INTRODUCTION...........................................4 INTRODUCTION.................................................4
    1.1 Terms.................................................6 Terms......................................................6
    1.2 Notational Conventions................................7 Conventions.....................................7

    2 PRINCIPALS.............................................7 PRINCIPALS...................................................7

    3 PRIVILEGES.............................................8 PRIVILEGES...................................................8
    3.1 DAV:read Privilege....................................9 Privilege.........................................9
    3.2 DAV:write Privilege...................................9 Privilege........................................9
    3.3 DAV:write-properties.................................10 DAV:write-properties.......................................9
    3.4 DAV:write-content....................................10 DAV:write-content.........................................10
    3.5 DAV:unlock...........................................10 DAV:unlock................................................10
    3.6 DAV:read-acl Privilege...............................11 Privilege....................................10
    3.7 DAV:read-current-user-privilege-set Privilege........11 Privilege.............10
    3.8 DAV:write-acl Privilege..............................11 Privilege...................................11
    3.9 DAV:delete Privilege.................................11 DAV:bind Privilege........................................11
    3.10 DAV:all Privilege..................................11 DAV:unbind Privilege.....................................11
    3.11 DAV:all Privilege........................................11
    3.12 Aggregation of Predefined Privileges...............12 Privileges.....................11

    4 PRINCIPAL PROPERTIES..................................12 PROPERTIES........................................12
    4.1 DAV:alternate-URI-set................................12 DAV:alternate-URI-set.....................................12
    4.2 DAV:principal-URL....................................13 DAV:principal-URL.........................................12
    4.3 DAV:group-member-set.................................13 DAV:group-member-set......................................12
    4.4 DAV:group-membership.................................13 DAV:group-membership......................................13

    5 ACCESS CONTROL PROPERTIES.............................13 PROPERTIES...................................13
    5.1 DAV:owner............................................14 DAV:owner.................................................13
     5.1.1 Example: Retrieving DAV:owner....................14 DAV:owner..........................13
     5.1.2 Example: An Attempt to Set DAV:owner.............15 DAV:owner...................14
    5.2 DAV:supported-privilege-set..........................16 DAV:supported-privilege-set...............................15
     5.2.1 Example: Retrieving a List of Privileges Supported on
           a Resource
       16 Resource.............................................16
    5.3 DAV:current-user-privilege-set.......................19 DAV:current-user-privilege-set............................18
     5.3.1 Example: Retrieving the User's Current Set of Assigned
   Privileges..............................................19
     Privileges...................................................19
    5.4 DAV:acl..............................................20 DAV:acl...................................................20
     5.4.1 ACE Principal....................................20 Principal..........................................20
     5.4.2 ACE Grant and Deny...............................21 Deny.....................................21
     5.4.3 ACE Protection...................................22 Protection.........................................21
     5.4.4 ACE Inheritance..................................22 Inheritance........................................21
     5.4.5 Example: Retrieving a Resource's Access Control List    22 ..22
    5.5 DAV: acl-restrictions................................24 acl-restrictions.....................................23
     5.5.1 DAV:grant-only...................................24

  Clemm, et al.                                       [Page 2] DAV:grant-only.........................................23
     5.5.2 DAV:no-invert ACE Constraint.....................24 Constraint...........................24
     5.5.3 DAV:deny-before-grant............................24 DAV:deny-before-grant..................................24
     5.5.4 Required Principals..............................24 Principals....................................24
     Example: Retrieving DAV:acl-restrictions................25 DAV:acl-restrictions.............     ...24
    5.6 DAV:inherited-acl-set................................26 DAV:inherited-acl-set.....................................25
    5.7 DAV:principal-collection-set.........................26 DAV:principal-collection-set..............................25
     5.7.1 Example: Retrieving DAV:principal-collection-set.27 DAV:principal-collection-set.......26
    5.8 Example: PROPFIND to retrieve access control properties28 properties...27

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    6 ACL EVALUATION........................................31 EVALUATION..............................................30

    7 ACCESS CONTROL AND EXISTING METHODS...................32 METHODS.........................31
    7.1 OPTIONS..............................................32 ANY HTTP METHOD...........................................32
     7.1.1 Error Handling.........................................32
    7.2 OPTIONS...................................................32
     7.2.1 Example - OPTIONS................................32
  7.2 MOVE.................................................33 OPTIONS......................................33
    7.3 COPY.................................................33 MOVE......................................................33
    7.4 LOCK.................................................33 COPY......................................................33
    7.5 LOCK......................................................33

    8 ACCESS CONTROL METHODS................................33 METHODS......................................33
    8.1 ACL..................................................33 ACL.......................................................33
     8.1.1 ACL Preconditions................................34 Preconditions......................................34
     8.1.2 Example: the ACL method..........................35 method................................35
     8.1.3 Example: ACL method failure due to protected ACE conflict    36
           conflict...............................................36
     8.1.4 Example: ACL method failure due to an inherited ACE conflict 37
           conflict...............................................37
     8.1.5 Example: ACL method failure due to an attempt to set
           grant and deny in a single ACE....................................38 ACE.........................38

    9 ACCESS CONTROL REPORTS................................39 REPORTS......................................39
    9.1 REPORT Method........................................39 Method.............................................39
    9.2 DAV:acl-principal-prop-set Report....................40 Report.........................39
     9.2.1 Example: DAV:acl-principal-prop-set Report.......41 Report.............40
    9.3 DAV:principal-match REPORT...........................42 REPORT................................42
     9.3.1 Example: DAV:principal-match REPORT..............43 REPORT....................43
    9.4 DAV:principal-property-search REPORT.................44 REPORT......................43
     9.4.1 Matching.........................................46 Matching...............................................45
     9.4.2 Example: successful DAV:principal-property-search REPORT 46
   9.4.3 Example: Unsuccessful DAV:principal-property-search REPORT   48
           REPORT.................................................46
    9.5 DAV:principal-search-property-set REPORT.............49 REPORT..................48
     9.5.1 Example: DAV:principal-search-property-set REPORT50 REPORT......49

    10  XML PROCESSING.......................................51 PROCESSING............................................50

    11  INTERNATIONALIZATION CONSIDERATIONS..................51 CONSIDERATIONS.......................50

    12  SECURITY CONSIDERATIONS..............................52 CONSIDERATIONS...................................51
    12.1 Increased Risk of Compromised Users................52 Users......................51
    12.2 Risks of the DAV:read-acl and
         DAV:current-user-privilege-set
  Privileges...............................................53 Privileges................51
    12.3 No Foreknowledge of Initial ACL....................53 ACL..........................52

    13  AUTHENTICATION.......................................54  AUTHENTICATION............................................52

    14  IANA CONSIDERATIONS..................................54

  Clemm, et al.                                       [Page 3] CONSIDERATIONS.......................................52

    15  INTELLECTUAL PROPERTY................................54 PROPERTY.....................................53

    16  ACKNOWLEDGEMENTS.....................................55  ACKNOWLEDGEMENTS..........................................53

    17  REFERENCES...........................................55  REFERENCES................................................53
    17.1 Normative References...............................55 References.....................................53

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    17.2 Informational References...........................56 References.................................54

    18  AUTHORS' ADDRESSES...................................57 ADDRESSES........................................55

    19  APPENDICES...........................................58  APPENDICES................................................56
    19.1 WebDAV XML Document Type Definition Addendum.......58 Addendum.............56
    19.2 WebDAV Method Privilege Table (Normative)..........60 (Normative)................58

    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 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

  Clemm, et al.                                       [Page 4] 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.

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 4] 
         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:
           . 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,
           . Role-based security (where a role can be seen as a
              dynamically defined group of principals),

  Clemm, et al.                                       [Page 5]
           . Specification of the ways an ACL on a resource is
              initialized,
           . Specification of an ACL that applies globally to all
              resources, rather than to a particular resource.
           . Creation and maintenance of resources representing people or
              computational agents (principals), and groups of these.

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 5] 
         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 7.1.
         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 (Section 19.1) provides an XML Document Type Definition
         (DTD) for the XML elements defined in the specification.

    1.1 Terms

         This draft 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

  Clemm, et al.                                       [Page 6]
         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) (non-
         abstract) privileges for a particular principal.

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 6] 
       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.

  Clemm, et al.                                       [Page 7]
         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.

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 7] 
    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 5.4.1).  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- 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 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

  Clemm, et al.                                       [Page 8]
         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
         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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 8] 
         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 [WEBDAV]), so effective write access requires that
         both write privileges and write locking requirements are
         satisfied.  Any

  Clemm, et al.                                       [Page 9] 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

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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 9] 
         <!ELEMENT write-properties EMPTY>

    3.4 DAV:write-content

         The DAV:write-content privilege controls methods that modify the
         content or (in the case of a collection) membership of the
         resource, such as PUT and DELETE.  Any implementation-defined
         privilege that also controls access to content or alteration of
         collection membership 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 or DELETE.
         <!ELEMENT write-content EMPTY>

    3.5 DAV:unlock

         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.

  Clemm, et al.                                      [Page 10]
         <!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
         writeable.
         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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 10] 
         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:delete DAV:bind Privilege

         The DAV:delete DAV:bind privilege controls use of the DELETE allows a method on to add a new member URL to
         the specified resource.  You must also have DAV:write-content on the collection containing the resource (for example via PUT or MKCOL).  It is
         ignored for resources that are not collections.
         <!ELEMENT bind EMPTY>

    3.10DAV:unbind Privilege

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

  3.10DAV:all

    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>

  Clemm, et al.                                      [Page 11] 
  3.11Aggregation

    3.12 Aggregation of Predefined Privileges

         Server implementations are free to aggregate the predefined
         privileges (defined above in Sections 3.1-3.9) 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.

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 11] 
         DAV:write MUST contain 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 [RFC2589] to retrieve additional machine-readable
         directory

  Clemm, et al.                                      [Page 12] 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*)>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 12] 
    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
         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.

  Clemm, et al.                                      [Page 13]
         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 protected 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.

         <!ELEMENT owner (href)>

  5.1.1Example:

    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 <<

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 13] 
         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="jim@webdav.org", 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>

  Clemm, et al.                                      [Page 14]
                     <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>

  5.1.2Example:

    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, the server 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, and Section 11 of [RFC2518] describes the Multi-
         Status response.
         >> Request <<

         PROPPATCH /papers/ HTTP/1.1
         Host: www.example.com
         Content-type: text/xml; charset="utf-8"

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 14] 
         Content-Length: xxx
         Depth: 0
         Authorization: Digest username="jim",
            realm="jim@webdav.org", 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>

  Clemm, et al.                                      [Page 15]
                  <D:prop><D:owner/></D:prop>
                  <D:status>HTTP/1.1 403 Forbidden</D:status>
                  <D:responsedescription>
                    Failure to set protected property (DAV:owner)
                  </D:responsedescription>
               </D:propstat>
            </D:response>
         </D:multistatus>

    5.2 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>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 15] 
         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.

  5.2.1Example:

    5.2.1 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

  Clemm, et al.                                      [Page 16]
         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 3.11), 3.12), and many
         possible privilege trees are possible.

         >> Request <<

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 16] 
         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="gclemm@webdav.org", 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>

  Clemm, et al.                                      [Page 17]
             <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 xml:lang="en">
                       Any operation</D:description>
                     <D:supported-privilege>
                       <D:privilege> <D:read/> </D:privilege>
                       <D:description xml:lang="en">Read 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 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 xml:lang="en">
                           Read current user privilege set property</D:description> property
                         </D:description>
                       </D:supported-privilege>
                       </D:supported-privilege>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 17] 
                       <D:supported-privilege>
                       <D:privilege> <D:write/> </D:privilege>
                       <D:description xml:lang="en">Write xml:lang="en">
                        Write any object</D:description>
                       <D:supported-privilege>
                         <D:privilege> <D:write-acl/> </D:privilege>
                         <D:description xml:lang="en">Write 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 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 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 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>

  Clemm, et al.                                      [Page 18]
         </D:multistatus>

    5.3 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-

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 18] 
         privilege-set property MUST identify a non-abstract privilege from
         the DAV:supported-privilege-set property.

  5.3.1Example:

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

         Continuing the example from Section 5.2.1, 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 DAV:read-current-
         user-privilege-set privileges (see Section 5.2.1), the principal
         with username "khare" can read the ACL property, and the DAV:current-
       user-privilege-set
         DAV:current-user-privilege-set property. However, the DAV:all,
         DAV:read-acl, DAV:write-acl and DAV:read-current-user-privilege-set DAV:read-current-user-privilege-
         set privileges are not listed in the value of DAV:current-user-privilege-set, 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="khare@webdav.org", nonce="...",
            uri="/papers/", response="...", opaque="..."

         <?xml version="1.0" encoding="utf-8" ?>

  Clemm, et al.                                      [Page 19]
         <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>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 19] 
                 </D:current-user-privilege-set>
               </D:prop>
               <D:status>HTTP/1.1 200 OK</D:status>
             </D:propstat>
           </D:response>
         </D:multistatus>

    5.4 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 (invert | principal, (grant|deny), protected?,
         inherited?)>

  5.4.1ACE

    5.4.1 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.

  Clemm, et al.                                      [Page 20]
         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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 20] 
         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>

         Alternately, 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>

         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>

  5.4.2ACE

    5.4.2 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+)>

  Clemm, et al.                                      [Page 21]
         <!ELEMENT deny (privilege+)>
         <!ELEMENT privilege ANY>

  5.4.3ACE

    5.4.3 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>

  5.4.4ACE

    5.4.4 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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 21] 
         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)>

  5.4.5Example:

    5.4.5 Example: Retrieving a Resource's Access Control List

         Continuing the example from Sections 5.2.1 and 5.3.1, 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 5.2.1), 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

  Clemm, et al.                                      [Page 22]
         Host: www.example.com
         Content-type: text/xml; charset="utf-8"
         Content-Length: xxx
         Depth: 0
         Authorization: Digest username="masinter",
            realm="webdav.org", nonce="...",
            uri="/papers/", response="...", opaque="..."

       <?xml version="1.0" encoding="utf-8" ?>

         <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

       <?xml version="1.0" encoding="utf-8" ?>

         <D:multistatus xmlns:D="DAV:">
           <D:response>
             <D:href>http://www.example.com/papers/</D:href>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 22] 
             <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>

  Clemm, et al.                                      [Page 23]

    5.5 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?, deny-before-
         grant?, required-principal?)>

  5.5.1DAV:grant-only

    5.5.1 DAV:grant-only

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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 23] 
         <!ELEMENT grant-only EMPTY>

  5.5.2DAV:no-invert

    5.5.2 DAV:no-invert ACE Constraint

         This element indicates that ACEs with the <invert> element are not
         allowed.
         <!ELEMENT no-invert EMPTY>

  5.5.3DAV:deny-before-grant

    5.5.3 DAV:deny-before-grant

         This element indicates that all deny ACEs must precede all grant
         ACEs.
         <!ELEMENT deny-before-grant EMPTY>

  5.5.4Required

    5.5.4 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*)>

  Clemm, et al.                                      [Page 24]

         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>

          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="srcarter@webdav.org", nonce="...",
            uri="/papers/", response="...", opaque="..."

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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 24] 
         </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:principal-only-one-ace/>
                   <D:required-principal>
                     <D:all/>
                   </D:required-principal>
                 </D:acl-restrictions>

  Clemm, et al.                                      [Page 25]
               </D:prop>
               <D:status>HTTP/1.1 200 OK</D:status>
             </D:propstat>
           <D:response>
         </D:multistatus>

    5.6 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*)>

    5.7 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*)>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 25] 
         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

  Clemm, et al.                                      [Page 26]
         lists, due to the difficulty of getting the URL of a principal for
         use in an ACE.

  5.7.1Example:

    5.7.1 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="yarong@webdav.org", 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>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 26] 
         >> 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>

  Clemm, et al.                                      [Page 27]
               <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>

    5.8 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, 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@foo.org", 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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 27] 
         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>

  Clemm, et al.                                      [Page 28]
                 <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:privilege> <A:delete/> <A:unbind/> </D:privilege>
                     <D:description xml:lang="en">Delete xml:lang="en">Remove binding to an
         object</D:description>
                   </D:supported-privilege>
                 </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>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 28] 
               </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/marketing</D:href>
                 </D:principal>
                 <D:deny>
                   <D:privilege> <D:read/> </D:privilege> </D:deny>
               </D:ace>

  Clemm, et al.                                      [Page 29]
               <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):

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 29] 
            [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/marketing are denied the DAV:read
         privilege.  In this example, the principal URL identifies a group.

  Clemm, et al.                                      [Page 30]
         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 [NFSV4]).  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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 30] 
         file’s group and for the world.  An ACL for UNIX permissions of "r--rw-r--
       "might
         "r--rw-r--"might be constructed like:
               <D:acl>
               <D:ace>
               <D:principal><D:property><D:owner/></D:property></D:principal>
                 <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: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: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>

  Clemm, et al.                                      [Page 31]
                 <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:principal-only-one-ace/>
              <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.

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 31] 
    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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 32] 
         supports all MUST level requirements and REQUIRED features
         specified in this document.

  7.1.1Example

    7.2.1 Example - OPTIONS

         >> Request <<

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

         >> Response <<

  Clemm, et al.                                      [Page 32]

           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.

  7.2

    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.

  7.3

    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.

  7.4

    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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 33] 
         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 5.4) 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

  Clemm, et al.                                      [Page 33] 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.

  8.1.1ACL

    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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 34] 
         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

  Clemm, et al.                                      [Page 34]
         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 5.5.1).
         (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 6.3.4).
         (DAV:no-abstract): The ACL request MUST NOT attempt to grant or
         deny an abstract privilege (see Section 5.2).
         (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 5.5.4).
         (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.

  8.1.2Example:

    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.,

    Clemm, et al. Hopkins, Sedlar, Whitehead                                [Page 35] 
         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@foo.org", 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

  8.1.3Example:

    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 5.4.3)
         granting DAV:owner the DAV:read and DAV:write privileges. The principal

    Clemm, et al. Hopkins, Sedlar, Whitehead                                [Page 36] 
         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@foo.org", 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>

  8.1.4Example:

    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.

  Clemm, et al.                                      [Page 37]
         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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 37] 
         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@foo.org", 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 xmlns:D="DAV:"/>
         </D:error>

  8.1.5Example:

    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. 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.

  Clemm, et al.                                      [Page 38]
         >> Request <<

         ACL /diamond/engagement-ring.gif HTTP/1.1

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 38] 
         Host: www.example.com
         Content-Type: text/xml; charset="utf-8"
         Content-Length: xxxx
         Authorization: Digest username="ygoland",
            realm="users@foo.org", 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]).

  Clemm, et al.                                      [Page 39]

    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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 39] 
         properties specified in the REPORT request body. In the case where
         a principal URL appears multiple times, the DAV:acl-principal-prop-
       set 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.

  Clemm, et al.                                      [Page 40] 
  9.2.1Example:

    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.

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 40] 
         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>

  Clemm, et al.                                      [Page 41]
           </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>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 41] 
    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-

  Clemm, et al.                                      [Page 42]
         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.

  9.3.1Example:

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 42] 
    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="gclemm@webdav.org", 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>

  Clemm, et al.                                      [Page 43]
         </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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 43] 
         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 client can discover the set of
       searchable search requesting properties by using the DAV:principal-search-property-
       set REPORT, defined in Section 9.5. 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 case-
           insensitive matching is non-
       trivial. non-trivial. Implementors of servers
           that do perform substring matching are strongly encouraged to
           consult [CaseMap], especially Section 2.3 ("Caseless
           Matching"), for guidance when implementing their
       case-insensitive 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.

  Clemm, et al.                                      [Page 44]
         <!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:prinicipal-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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 44] 
         <!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.
         The response body for an unsuccessful DAV:principal-property-search DAV:principal-property-
         search REPORT request MUST contain, after the XML element
         indicating the failed precondition or postcondition, a DAV:prop
         element containing the property that caused the pre/postcondition
         to fail.
         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:

       (DAV:property-must-be-searchable): All properties specified in the
       DAV:principal-property-search REPORT must be searchable.
         None
       Postconditions:

  Clemm, et al.                                      [Page 45]
         (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.

  9.4.1Matching

    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 marshalling 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".

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 45] 
         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/", marshalled 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}.

  9.4.2Example:

    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

  Clemm, et al.                                      [Page 46]
         "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>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 46] 
             <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

  Clemm, et al.                                      [Page 47]

         <?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>

  9.4.3Example: Unsuccessful DAV:principal-property-search REPORT

       In this example, the client requests a search on the non-searchable
       property "phone" in the namespace "http://www.example.com/ns/".
       The response is a 403 (Forbidden), with a response body containing
       a DAV:property-must-be-searchable XML element as the value of a
       DAV:error XML element.

       >> Request <<

       REPORT /users/ HTTP/1.1
               </D:prop>

    Clemm, et al. Hopkins, Sedlar, Whitehead                                [Page 48] 
       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 xmlns:B="http://www.example.com/ns/">
             <B:phone/> 47] 
               <D:status>HTTP/1.1 200 OK</D:status>
             </D:propstat>
             <D:propstat>
               <D:prop>
                 <B:salary/>
               </D:prop>
           <D:match>232</D:match>
         </D:property-search>
       </D:principal-property-search>

       >> Response <<

       HTTP/1.1
               <D:status>HTTP/1.1 403 Forbidden
       Content-Type: text/xml; charset=utf-8
       Content-Length: xxxx

       <?xml version="1.0" encoding="utf-8" ?>
       <D:error xmlns:D="DAV:">
         <D:property-must-be-searchable>
           <D:prop xmlns:B="http://www.example.com/ns/">
             <B:phone/>
           </D:prop>
         </D:property-must-be-searchable>
       </D:error> 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

  Clemm, et al.                                      [Page 49] 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 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 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.

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 48] 
         <!ELEMENT principal-search-property-set (principal-search-property*) (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 >

  9.5.1Example:

    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 <<

  Clemm, et al.                                      [Page 50]
         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>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 49] 
             <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
         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

  Clemm, et al.                                      [Page 51] 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 [UTF-8] 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. Futhermore, 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 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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 50] 
         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.

  12.1Increased

    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

  Clemm, et al.                                      [Page 52]
         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.

  12.2Risks

    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-writeable. 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, writeable 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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 51] 
         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.

  12.3No

    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

  Clemm, et al.                                      [Page 53] 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.

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 52] 
    15 INTELLECTUAL PROPERTY

         The following notice is copied from RFC 2026, section 10.4, and
         describes the position of the IETF concerning intellectual
         property claims made against this document.
         The IETF takes no position regarding the validity or scope of any
         intellectual property or other rights that might be claimed to
         pertain to the implementation or use other technology described in
         this document or the extent to which any license under such rights
         might or might not be available; neither does it represent that it
         has made any effort to identify any such rights.  Information on
         the IETF's procedures with respect to rights in standards-track
         and standards-related documentation can be found in BCP-11. Copies
         of claims of rights made available for publication and any
         assurances of licenses to be made available, or the result of an
         attempt made to obtain a general license or permission for the use
         of such proprietary rights by implementers or users of this
         specification can be obtained from the IETF Secretariat.
         The IETF invites any interested party to bring to its attention
         any copyrights, patents or patent applications, or other
         proprietary rights that may cover technology that may be required
         to practice

  Clemm, et al.                                      [Page 54] this standard.  Please address the information to the
         IETF Executive Director.

    16 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, Julian Reschke, 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.

    17 REFERENCES

  17.1Normative

    17.1 Normative References

         [RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
         Requirement Levels." RFC 2119, BCP 14, March, 1997.
         [REC-XML] T. Bray, J. Paoli, C.M. Sperberg-McQueen, "Extensible
         Markup Language (XML)." World Wide Web Consortium Recommendation
         REC-xml.http://www.w3.org/TR/REC-xml

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 53] 
         [REC-XML-NAMES] T. Bray, D. Hollander, A. Layman, "Name Spaces in
         XML" World Wide Web Consortium Recommendation REC-xml-names.
         http://www.w3.org/TR/REC-xml-names/
         [RFC3253] G. Clemm, J. Amsden, T. Ellison, C. Kaler, J. Whitehead,
         "Versioning Extensions to WebDAV." RFC 3253, March 2002.
         [REC-XML-INFOSET] J. Cowan, R. Tobin, "XML Information Set." World
         Wide Web Consortium Recommendation REC-xml-infoset.
         http://www.w3.org/TR/xml-infoset/
         [RFC2616] R. Fielding, J. Gettys, J. C. Mogul, H. Frystyk, L.
         Masinter, P. Leach, and T. Berners-Lee, "Hypertext Transfer
         Protocol -- HTTP/1.1." RFC 2616, June, 1999.
         [RFC2617] J. Franks, P. Hallam-Baker, J. Hostetler, S. Lawrence,
         P. Leach, A. Luotonen, L. Stewart, "HTTP Authentication: Basic and
         Digest Access Authentication." RFC 2617, June, 1999.

  Clemm, et al.                                      [Page 55]
         [RFC2518] Y. Goland, E. Whitehead, A. Faizi, S. R. Carter, D.
         Jensen, "HTTP Extensions for Distributed Authoring -- WEBDAV." RFC
         2518, February, 1999.
         [RFC2368] P. Hoffman, L. Masinter, J. Zawinski, "The mailto URL
         scheme." RFC 2368, July, 1998.
         [RFC3023] M. Murata, S. St.Laurent, D. Kohn, "XML Media Types."
         RFC 3023, January, 2001.
         [RFC3010] S. Shepler, B. Callaghan, D. Robinson, R. Thurlow, C.
         Beame, M. Eisler, D.Noveck "NFS version 4 Protocol." RFC 3010,
         December 2000.
          [UTF-8] F. Yergeau, "UTF-8, a transformation format of Unicode
         and ISO 10646." RFC 2279, January, 1998.

  17.2Informational

    17.2 Informational References

         [RFC2026] S.Bradner, "The Internet Standards Process - Revision
         3." RFC 2026, BCP 9. Harvard, October, 1996.
         [RFC2255] T. Howes, M. Smith, "The LDAP URL Format." RFC 2255.
         Netscape, December, 1997.
         [RFC2251] M. Wahl, T. Howes, S. Kille, "Lightweight Directory
         Access Protocol (v3)." RFC 2251. Critical Angle, Netscape, Isode,
         December, 1997.
         [CaseMap] M. Davis, "Case Mappings", Unicode Standard Annex #21,
         March 26, 2001.  http://www.unicode.org/unicode/reports/tr21

    Clemm, et al. Hopkins, Sedlar, Whitehead                                [Page 56] 54] 
    18 AUTHORS' ADDRESSES

         Geoffrey Clemm
         IBM
         20 Maguire Road
         Lexington, MA 02421
         Email: geoffrey.clemm@us.ibm.com

         Anne Hopkins
         Microsoft Corporation
         One Microsoft Way
         Redmond, WA 98052
         Email: annehop@microsoft.com

         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
         Baskin Engineering
         1156 High Street
         Santa Cruz, CA 95064
         Email: ejw@cse.ucsc.edu

    Clemm, et al. Hopkins, Sedlar, Whitehead                                [Page 57] 55] 
    19 APPENDICES

  19.1WebDAV

    19.1 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 -->

         <!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 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 prop?)>
         <!ELEMENT prop (see [RFC2518], section 12.11)>

         <!-- DAV:supported-privilege-set Property (Section 5.2) -->

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

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

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

  Clemm, et al.                                      [Page 58]

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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 56] 
         <!-- DAV:acl Property (Section 5.4) -->

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

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

         <!ELEMENT prop (see [RFC2518], section 12.11)>
         <!ELEMENT all EMPTY>
         <!ELEMENT authenticated EMPTY>
         <!ELEMENT unauthenticated EMPTY>
         <!ELEMENT property ANY>
         <!ELEMENT self EMPTY>

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

         <!ELEMENT protected EMPTY>

         <!ELEMENT inherited (href)>

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

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

         <!-- DAV:principal-collection-set Property (Section 5.6) -->

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

         <!-- DAV:acl-semantics Property (Section 6) -->

         <!ELEMENT acl-semantics (ace-combination?, ace-ordering?, allowed-ace?, allowed-
         ace?, required-principal?)>

         <!ELEMENT ace-combination
          (first-match | all-grant-before-any-deny | specific-deny-overrides-grant)> specific-deny-
         overrides-grant)>
         <!ELEMENT first-match EMPTY>
         <!ELEMENT all-grant-before-any-deny EMPTY>
         <!ELEMENT specific-deny-overrides-grant EMPTY>

         <!ELEMENT ace-ordering (deny-before-grant)? >
         <!ELEMENT deny-before-grant EMPTY>

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 57] 
         <!ELEMENT allowed-ace (grant-only |

  Clemm, et al.                                      [Page 59]
                         no-invert)*>
         <!ELEMENT grant-only EMPTY>
         <!ELEMENT no-invert EMPTY>

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

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

  19.2WebDAV

    19.2 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

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 58] 
    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
    sub-privilege aggregated under the indicated privilege to control
    access.

  Clemm, et al.                                      [Page 60]  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 parent coll if resource
       doesn't already exist, or on existing target resource
       otherwise)
     PUT (no target exists)  <D:bind> on parent collection of target
     PROPPATCH          <D:write-properties>
     ACL                <D:write-acl>
     PROPFIND           <D:read> (plus <read-acl> <D:read-acl> and
       <read-current-user-privilege-set>
                        <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:write-content> <D:unbind> on source&target coll, plus
  <dav:read> source collection and <D:bind>
    on the resource being moved MAY be required target collection
     MOVE (target exists)    As above, plus <D:delete> <D:unbind> on the resource to be
  overwritten target
    collection
     DELETE   <D:delete>, <D:write-content>             <D:unbind> on parent collection
     LOCK (target exists)    <D:write-content>
     LOCK (no target exists) <D:bind> on parent collection
     MKCOL    <D:write-content> (on              <D:bind> on parent coll) collection
     UNLOCK             <D:unlock>
     CHECKOUT      <D:write>           <D:write-properties >
     CHECKIN  <D:write>            <D:write-properties >
     REPORT             <D:read> (on all referenced resources)
     VERSION-CONTROL    <D:write>    <D:write-properties>
     MERGE              <D:write-content>
     MKWORKSPACE        <D:write-content> on parent collection
     BASELINE-CONTROL   <D:write>   <D:write-properties> and <D:write-content>
     MKACTIVITY         <D:write-content> on parent collection

    Clemm, Hopkins, Sedlar, Whitehead                                [Page 59]