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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 3744

   INTERNET-DRAFT                   Geoffrey Clemm, Rational Software
   draft-ietf-webdav-acl-06         Anne Hopkins, Microsoft Corporation
                                    Eric Sedlar, Oracle Corporation
                                    Jim Whitehead, U.C. Santa Cruz
   
   Expires December 21, 2001        June 21, 2001
   
   
   
                      WebDAV Access Control Protocol
   
   
   
   Status of this Memo
   
   This document is an Internet-Draft and is in full conformance with
   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 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
   http://www.ietf.org/shadow.html.
   
   Abstract
   
   This document specifies a set of methods, headers, and message
   bodies that define Access Control extensions to the WebDAV
   Distributed Authoring Protocol. This protocol permits a client to
   remotely read and modify access control lists that instruct a server
   whether to grant or deny operations upon a resource (such as HTTP
   method invocations) by a given principal.
   
   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.webdav.org/acl/, and
   http://www.ics.uci.edu/pub/ietf/webdav/.
   
   
   
   
   
   
   
   
   
   
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   Table of Contents
   
   1 INTRODUCTION...................................................4
   1.1  Terms.......................................................5
   1.2  Notational Conventions......................................6
   
   2 PRINCIPALS.....................................................6
   
   3 PRIVILEGES.....................................................7
   3.1  DAV:read Privilege..........................................8
   3.2  DAV:write Privilege.........................................8
   3.3  DAV:read-acl Privilege......................................9
   3.4  DAV:read-current-user-privilege-set Privilege...............9
   3.5  DAV:write-acl Privilege.....................................9
   3.6  DAV:all Privilege...........................................9
   3.7  Aggregation of Predefined Privileges........................9
   
   4 PRINCIPAL PROPERTIES..........................................10
   4.1  DAV:alternate-URL..........................................10
   
   5 ACCESS CONTROL PROPERTIES.....................................10
   5.1  DAV:owner..................................................11
    5.1.1 Example: Retrieving DAV:owner............................11
    5.1.2 Example: An Attempt to Set DAV:owner.....................12
   5.2  DAV:supported-privilege-set................................13
    5.2.1 Example: Retrieving a List of Privileges Supported on a
          Resource.................................................14
   5.3  DAV:current-user-privilege-set.............................15
    5.3.1 Example: Retrieving the User's Current Set of Assigned
          Privileges...............................................16
   5.4  DAV:acl....................................................17
    5.4.1 ACE Principal............................................17
    5.4.2 ACE Grant and Deny.......................................18
    5.4.3 ACE Protection...........................................18
    5.4.4 ACE Inheritance..........................................18
    5.4.5 Example: Retrieving a Resource's Access Control List.....19
   5.5  DAV:acl-semantics..........................................20
    5.5.1 Example: Retrieving DAV:acl-semantics....................21
   5.6  DAV:principal-collection-set...............................22
    5.6.1 Example: Retrieving DAV:principal-collection-set.........22
   5.7  Example: PROPFIND to retrieve access control properties....23
   
   6 ACL SEMANTICS.................................................27
   6.1  ACE Combination............................................27
    6.1.1 DAV:first-match ACE Combination..........................27
    6.1.2 DAV:all-grant-before-any-deny ACE Combination............27
    6.1.3 DAV:specific-deny-overrides-grant ACE Combination........27
   6.2  ACE Ordering...............................................28
    6.2.1 DAV:deny-before-grant ACE Ordering.......................28
   6.3  Allowed ACE................................................28
    6.3.1 DAV:principal-only-one-ace ACE Constraint................28
    6.3.2 DAV:grant-only ACE Constraint............................28
   6.4  Required Principals........................................28
   
   
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   7 ACCESS CONTROL AND EXISTING METHODS...........................29
   7.1  OPTIONS....................................................29
    7.1.1 Example - OPTIONS........................................29
   7.2  MOVE.......................................................29
   7.3  COPY.......................................................29
   
   8 ACCESS CONTROL METHODS........................................29
   8.1  ACL........................................................29
    8.1.1 ACL Preconditions........................................30
    8.1.2 Example: the ACL method..................................31
    8.1.3 Example: ACL method failure due to protected ACE
          conflict ................................................32
    8.1.4 Example: ACL method failure due to an inherited ACE
          conflict ................................................33
    8.1.5 Example: ACL method failure due to an attempt to set
          grant and deny in a single ACE ..........................34
   
   9 ACCESS CONTROL REPORTS........................................35
   9.1  REPORT Method..............................................35
   9.2  DAV:acl-principal-props Report.............................36
    9.2.1 Example: DAV:acl-principal-props Report..................36
   9.3  DAV:principal-match REPORT.................................37
    9.3.1 Example: DAV:principal-match REPORT......................38
   
   10  XML PROCESSING..............................................39
   
   11  INTERNATIONALIZATION CONSIDERATIONS.........................39
   
   12  SECURITY CONSIDERATIONS.....................................40
   12.1 Increased Risk of Compromised Users........................40
   12.2 Risks of the DAV:read-acl and DAV:current-user-privilege-set
        Privileges.................................................40
   12.3 No Foreknowledge of Initial ACL............................41
   
   13  AUTHENTICATION..............................................41
   
   14  IANA CONSIDERATIONS.........................................42
   
   15  INTELLECTUAL PROPERTY.......................................42
   
   16  ACKNOWLEDGEMENTS............................................42
   
   17  REFERENCES..................................................43
   17.1 Normative References.......................................43
   17.2 Informational References...................................43
   
   18  AUTHORS' ADDRESSES..........................................43
   
   19  APPENDICIES.................................................44
   19.1 XML Document Type Definition...............................44
   
   20  NOTE TO RFC EDITOR..........................................46
   
   
   
   
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   1  INTRODUCTION
   
        The goal of the WebDAV access control extensions is to provide
        an interoperable mechanism for handling discretionary access
        control for content in 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 how you can access 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 "how" is 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.
   
        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 collection of principals),
   
          * 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.
   
        This specification is organized as follows. Section 1.1 defines
        key concepts used throughout the specification, and is followed
        by 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 semantics of
        access control lists are described in Section 6, including
        sections on ACE combination (Section 6.1), ACE ordering
   
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        (Section 6.2), and principals required to be present in an ACE
        (Section 6.4). Client discovery of access control capability
        using OPTIONS is described in Section 7.1, and the access
        control setting method, ACL, is specified in Section 8.
        Internationalization considerations (Section 11) and security
        considerations (Section 12) 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.
   
      principal collection
   
        A "principal collection" is a group of principals, and is
        represented in this protocol by a WebDAV collection containing
        HTTP resources that represent principals, and principal
        collections.
   
      privilege
   
        A "privilege" controls access to a particular set of HTTP
        operations on a resource.
   
      aggregate privilege
   
        An "aggregate privilege" is a privilege that contains a set of
        other privileges.
   
      abstract privilege
   
        The modifier "abstract", when applied to a privilege, means the
        privilege cannot be set in an access control element (ace).
   
      access control list (ACL)
   
        An "ACL" is a list of access control elements that define
        access control to a particular resource.
   
      access control element (ace)
   
        An "ace" either grants or denies a particular set of (non-
        abstract) privileges for a particular principal.
   
   
   
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      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].
   
   2  PRINCIPALS
   
        A principal is a network resource that represents a distinct
        human or computational actor that initiates access to network
        resources. On many implementations, users and groups are
        represented as principals; other types of principals are also
        possible. A URI of any scheme MAY be used to identify a
        principal resource. However, servers implementing this
        specification MUST expose principal resources at an http(s)
        URL, which is a privileged scheme that points to resources that
        have additional properties, as described in Section 4. So, a
        principal resource can have multiple URI identifiers, 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 or may not be a collection.  If a
        person or computational agent matches a principal resource that
        is contained by a collection principal, they also match the
        collection principal. This definition is recursive, and hence
        if a person or computational agent matches a collection
        principal that is the child of another collection principal,
        they also match the parent collection principal. Membership in
        a collection principal is also recursive, so a principal in a
        collection principal GRPA contained by collection principal
   
   
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        GRPB is a member of both GRPA and GRPB. Implementations not
        supporting recursive membership in principal collections can
        return an error if the client attempts to bind collection
        principals into other collection principals.
   
        Servers that support aggregation of principals (e.g. groups of
        users or other groups) MUST manifest them as collection
        principals. At minimum, principals and collection principals
        MUST support the OPTIONS and PROPFIND methods.
   
           Implementer's Note: Collection principals are first and
           foremost WebDAV collections. Therefore they contain
           resources as members. Since there is no requirement that all
           members of a collection principal need be principals, it is
           possible for a collection principal to have non-principals
           as members. When enumerating the principals-only membership
           of a collection principal, it is necessary to retrieve the
           DAV:resourcetype property and check it for the DAV:principal
           XML element (described in Section 4). If the DAV:principal
           XML element is not present, the resource is not a principal
           and may be ignored for the purposes of determining the
           principals-only membership of the collection principal.
   
           For example, the collection principal /FOO/ has two members,
           Bar and Baz. Bar is a principal but Baz is not. Therefore
           when determining which principals belong to the collection
           principal /FOO/, a client would enumerate the membership
           using PROPFIND while asking for the DAV:resourcetype
           property, and see that only Bar has the DAV:principal XML
           element. Therefore, only Bar is the only principal that is a
           member of the collection principal /FOO/.
   
   3  PRIVILEGES
   
        Ability to perform a given method on a resource SHOULD 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 SHOULD be denied any HTTP access to
        that resource.
   
        Privileges may be containers of other privileges, in which case
        they are termed aggregate privileges.  If a principal is
        granted or denied an aggregate privilege, it is semantically
        equivalent to granting or denying each of the aggregated
        privileges individually.  For example, an implementation may
        define add-member and remove-member privileges that control the
        ability to add and remove an internal member of a collection.
        Since these privileges control the ability to update the state
        of a collection, these privileges would be aggregated by the
        DAV:write privilege on a collection, and granting the DAV:write
        privilege on a collection would also grant the add-member and
        remove-member privileges.
   
   
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        Privileges may have the quality of being abstract, in which
        case they cannot be set in an ACE. Aggregate and non-aggregate
        privileges are both capable of being abstract. Abstract
        privileges are useful for modeling privileges that otherwise
        would not be exposed via the protocol. Abstract privileges also
        provide server implementations with flexibility in implementing
        the privileges defined in this specification.  For example, if
        a server is incapable of separating the read resource
        capability from the read ACL capability, it can still model the
        DAV:read and DAV:read-acl privileges defined in this
        specification by declaring them abstract, and containing them
        within a non-abstract aggregate privilege (say, read-all) that
        holds DAV:read, and DAV:read-acl. In this way, it is possible
        to set the aggregate privilege, read-all, thus coupling the
        setting of DAV:read and DAV:read-acl, but it is not possible to
        set DAV:read, or DAV:read-acl individually. Since aggregate
        privileges can be abstract, it is also possible to use abstract
        privileges to group or organize non-abstract privileges.
        Privilege containment loops are not allowed, hence a privilege
        MUST NOT contain itself. For example, DAV:read cannot contain
        DAV:read.
   
        The set of privileges that apply to a particular resource may
        vary with the DAV:resourcetype of the resource, as well as
        between different server implementations.  To promote
        interoperability, however, this specification defines a set of
        well-known privileges (e.g. DAV:read,DAV:write, DAV:read-acl,
        DAV:write-acl, DAV:read-current-user-privilege-set, and
        DAV:all), which can at least be used to classify the other
        privileges defined on a particular resource. The access
        permissions on null and lock-null resources (defined in
        [RFC2518], Sections 3 and 7.4) 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 and lock-null resources). On the transition from null or
        lock-null to a stateful resource, the initial access control
        list is set by the server's default ACL value policy (if any).
   
   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.
        Additionally, the read privilege MAY control the OPTIONS
        method.
   
        <!ELEMENT read EMPTY>
   
   3.2 DAV:write Privilege
   
        The write privilege controls methods that 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
   
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        [WEBDAV]), so effective write access requires that both write
        privileges and write locking requirements are satisfied.
   
        <!ELEMENT write EMPTY>
   
   3.3 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>
   
   3.4 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 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>
   
   3.5 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>
   
   3.6 DAV:all Privilege
   
        DAV:all is an aggregate privilege that contains the entire set
        of privileges that apply to the resource.
   
        <!ELEMENT all EMPTY>
   
   3.7 Aggregation of Predefined Privileges
   
        Server implementations are free to aggregate the predefined
        privileges (defined above in Sections 3.1-3.6) subject to the
        following limitations:
   
   
   
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        DAV:read-acl MUST NOT contain DAV:read, DAV:write, DAV:write-
        acl, 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, or DAV:write-acl.
   
   4  PRINCIPAL PROPERTIES
   
        Principals are manifested to clients as an HTTP resource,
        identified by a URL.  A principal MUST have a 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 empty XML element in the value of the
        DAV:resourcetype property in addition to all other reported
        elements. For example, a collection principal would report
        DAV:collection and DAV:principal elements. The element type
        declaration for DAV:principal is:
   
        <!ELEMENT principal EMPTY>
   
        This protocol defines the following additional property for a
        principal. Since it is expensive, for many servers, to retrieve
        access control information, the name and value of this property
        SHOULD NOT be returned by a PROPFIND allprop request (as
        defined in Section 12.14.1 of [RFC2518]).
   
   4.1 DAV:alternate-URL
   
        This protected property, if non-empty, contains the URIs of
        network resources with additional descriptive information about
        the principal. This property identifies one or more 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. Two potential uses for this property
        are to store an ldap [RFC2255] or mailto [RFC2368] scheme URL.
        Support for this property is REQUIRED, and the value is empty
        if no alternate URL exists for the principal. .
   
        <!ELEMENT alternate-URL (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
   
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        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.
   
        HTTP resources that support the WebDAV Access Control Protocol
        MUST contain the following properties. Null, and lock-null
        resources (described in Section 7.4 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)>
   
   
   5.1.1 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.webdav.org/papers/. The principal making the request
        is authenticated using Digest authentication. The value of
        DAV:owner is the URL http://www.webdav.org/_acl/users/gstein,
        wrapped in the DAV:href XML element.
   
        >> Request <<
   
        PROPFIND /papers/ HTTP/1.1
        Host: www.webdav.org
        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:owner/>
        </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:">
   
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           <D:response>
              <D:href>http://www.webdav.org/papers/</D:href>
              <D:propstat>
                 <D:status>HTTP/1.1 200 OK</D:status>
                 <D:prop>
                    <D:owner>
                     <D:href>
                       http://www.webdav.org/_acl/users/gstein
                     </D:href>
                    </D:owner>
                 </D:prop>
              </D:propstat>
           </D:response>
        </D:multistatus>
   
   5.1.2 Example: An Attempt to Set DAV:owner
   
        The following example shows a client request to modify the
        value of the DAV:owner property on the resource with URL
        http://www.webdav.org/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. [RFC2518], Section 8.2.1 describes
        PROPPATCH status code information, and Section 11 describes the
        Multi-Status response.
   
        >> Request <<
   
        PROPPATCH /papers/ HTTP/1.1
        Host: www.webdav.org
        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:propertyupdate xmlns:D="DAV:">
           <D:set>
              <D:prop>
                 <D:owner>
                   <D:href>
                     http://www.webdav.org/_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
   
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        <?xml version="1.0" encoding="utf-8" ?>
        <D:multistatus xmlns:D="DAV:">
           <D:response>
              <D:href>http://www.webdav.org/papers/</D:href>
              <D:propstat>
                 <D:status>HTTP/1.1 403 Forbidden</D:status>
                 <D:prop><D:owner/></D:prop>
              </D:propstat>
              <D:responsedescription>Failure to set protected property
        (DAV:owner)
              </D:responsedescription>
           </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>
   
        An abstract privilege of a resource 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.
   
        <!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.
   
   
   
   
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   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
        http://www.webdav.org/papers/. The value of the DAV:supported-
        privilege-set property is a tree of supported privileges:
   
          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)
   
   
        This privilege tree is not normative, and many possible
        privilege trees are possible.
   
   
   
        >> Request <<
   
        PROPFIND /papers/ HTTP/1.1
        Host: www.webdav.org
        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:supported-privilege-set/>
        </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.webdav.org/papers/</D:href>
            <D:propstat>
              <D:status>HTTP/1.1 200 OK</D:status>
              <D:prop>
                <D:supported-privilege-set>
   
   
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                  <D:supported-privilege>
                    <D:privilege> <D:all/> </D:privilege>
                    <D:abstract/>
                    <D:description>Any operation</D:description>
                    <D:supported-privilege>
                      <D:privilege> <D:read/> </D:privilege>
                      <D:description>Read any object</D:description>
                      <D:supported-privilege>
                        <D:privilege> <D:read-acl/> </D:privilege>
                        <D:abstract/>
                        <D:description>Read ACL</D:description>
                      </D:supported-privilege>
                    </D:supported-privilege>
                      <D:supported-privilege>
                        <D:privilege>
                          <D:read-current-user-privilege-set/>
                        </D:privilege>
                        <D:abstract/>
                        <D:description>Read current user privilege set
        property</D:description>
                      </D:supported-privilege>
                    <D:supported-privilege>
                      <D:privilege> <D:write/> </D:privilege>
                      <D:description>Write any object</D:description>
                      <D:supported-privilege>
                        <D:privilege> <D:write-acl/> </D:privilege>
                        <D:description>Write ACL</D:description>
                        <D:abstract/>
                      </D:supported-privilege>
                    </D:supported-privilege>
                  </D:supported-privilege>
                </D:supported-privilege-set>
              </D:prop>
            </D:propstat>
          </D:response>
        </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 is particularly useful for an access
        control user interface, which can be constructed without
        knowing the ACE combining semantics of the server. 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*)>
   
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        <!ELEMENT privilege ANY>
   
        If the current user is granted a specific privilege, that
        privilege must belong to the set of privileges that may be set
        on this resource. Therefore, each element in the DAV:current-
        user-privilege-set property MUST identify a non-abstract
        privilege from the DAV:supported-privilege-set property.
   
   5.3.1 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.webdav.org/papers/. The
        username of the principal making the request is ôkhareö, and
        Digest authentication is used in the request. The principal
        with username ôkhareö has been granted the DAV:read privilege.
        Since the DAV:read privilege contains the DAV:read-acl and
        DAV:read-current-user-privilege-set privileges (see Section
        5.2.1), the principal with username ôkhareö can read the ACL
        property, and the DAV:current-user-privilege-set property.
        However, the DAV:all, DAV:read-acl, DAV:write-acl and DAV:read-
        current-user-privilege-set privileges are not listed in the
        value of DAV:current-user-privilege-set, since (for this
        example) they are abstract privileges. DAV:write is not listed
        since the principal with username ôkhareö is not listed in an
        ACE granting that principal write permission.
   
        >> Request <<
   
        PROPFIND /papers/ HTTP/1.1
        Host: www.webdav.org
        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" ?>
        <D:propfind xmlns:D="DAV:">
          <D:current-user-privilege-set/>
        </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>
   
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            <D:href>http://www.webdav.org/papers/</D:href>
            <D:propstat>
              <D:status>HTTP/1.1 200 OK</D:status>
              <D:prop>
                <D:current-user-privilege-set>
                  <D:privilege> <D:read/> </D:privilege>
                </D:current-user-privilege-set>
              </D:prop>
            </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 (principal, (grant|deny), protected?,
        inherited?)>
   
   
   
   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.
   
        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.
   
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        <!ELEMENT unauthenticated EMPTY>
   
        DAV:all is the union of DAV:authenticated, and
        DAV:unauthenticated. For a given request, the user matches
        either DAV:authenticated, or DAV:unauthenticated, but not both
        (that is, DAV:authenticated and DAV:unauthenticated are
        disjoint sets).
   
        The current user matches a DAV:property principal in a DAV:acl
        property of a resource only if the value of the identified
        property of that resource contains at most one DAV:href XML
        element, the URI value of DAV:href identifies a principal, and
        the current user is authenticated as being (or being a member
        of) that principal.  For example, if the DAV:property element
        contained <DAV:owner/>, the current user would match the
        DAV:property principal only if the current user is
        authenticated as matching the principal identified by the
        DAV:owner property of the resource.
   
        <!ELEMENT property ANY>
   
        The current user matches DAV:self in a DAV:acl property of the
        resource only if that resource is a principal object and the
        current user is authenticated as being that principal or a
        member of that principal collection.
   
        <!ELEMENT self EMPTY>
   
   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+)>
        <!ELEMENT deny (privilege+)>
        <!ELEMENT privilege ANY>
   
   5.4.3 ACE Protection
   
        If an ACE contains a DAV:protected element, an ACL request
        without that ACE MUST fail.
   
        <!ELEMENT protected EMPTY>
   
   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.
   
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        Note that ACE inheritance is not the same as ACL
        initialization.  ACL initialization defines the ACL that a
        newly created resource will use (if not specified).  ACE
        inheritance refers to an ACE that is logically shared - where
        an update to the resource containing an ACE will affect the ACE
        of each resource that inherits that ACE.  The method by which
        ACLs are initialized or by which ACEs are inherited is not
        defined by this document.
   
        <!ELEMENT inherited (href)>
   
   5.4.5 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.webdav.org/papers/. There are two
        ACEs defined in this ACL:
   
        ACE #1: The principal collection identified by URL
        http://www.webdav.org/_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 ômaintainersö 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 ômaintainersö group) can
        read the DAV:acl property and the DAV:current-user-privilege-
        set property.
   
   
        >> Request <<
   
        PROPFIND /papers/ HTTP/1.1
        Host: www.webdav.org
        Content-type: text/xml; charset="utf-8"
        Content-Length: xxx
        Depth: 0
        Authorization: Digest username="masinter",
           realm="masinter@webdav.org", nonce="...",
           uri="/papers/", response="...", opaque="..."
   
        <?xml version="1.0" encoding="utf-8" ?>
        <D:propfind xmlns:D="DAV:">
          <D:acl/>
        </D:propfind>
   
   
        >> Response <<
   
        HTTP/1.1 207 Multi-Status
        Content-Type: text/xml; charset="utf-8"
   
   
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        Content-Length: xxx
   
        <?xml version="1.0" encoding="utf-8" ?>
        <D:multistatus xmlns:D="DAV:">
          <D:response>
            <D:href>http://www.webdav.org/papers/</D:href>
            <D:propstat>
              <D:status>HTTP/1.1 200 OK</D:status>
              <D:prop>
                <D:acl>
                  <D:ace>
                    <D:principal>
                      <D:href>
                        http://www.webdav.org/_acl/groups/maintainers/
                      </D:href>
                    </D:principal>
                    <D:grant>
                      <D:privilege> <D:write/> </D:privilege>
                    </D:grant>
                  </D:ace>
                  <D:ace>
                    <D:principal>
                      <D:href> <D:all/> </D:href>
                    </D:principal>
                    <D:grant>
                      <D:privilege> <D:read/> </D:privilege>
                    </D:grant>
                  </D:ace>
                </D:acl>
              </D:prop>
            </D:propstat>
          </D:response>
        </D:multistatus>
   
   
   5.5 DAV:acl-semantics
   
        This is a protected property that defines the ACL semantics.
        These semantics define how multiple ACEs that match the current
        user are combined, what are the constraints on how ACEs can be
        ordered, and which principals must have an ACE. A client user
        interface could use the value of this property to provide
        feedback to a human operator concerning the impact of proposed
        changes to an ACL. Alternately, a client can use this property
        to help it determine, before submitting an ACL method
        invocation, what ACL changes it needs to make to accomplish a
        specific goal (or whether that goal is even achievable on this
        server).
   
        Since it is not practical to require all implementations to use
        the same ACL semantics, the DAV:acl-semantics property is used
        to identify the ACL semantics for a particular resource.  The
        DAV:acl-semantics element is defined in Section 6.
   
   
   
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   5.5.1 Example: Retrieving DAV:acl-semantics
   
        In this example, the client requests the value of the DAV:acl-
        semantics property. Digest authentication provides credentials
        for the principal operating the client. In this example, the
        ACE combination semantics are DAV:first-match, described in
        Section 6.1.1, the ACE ordering semantics are not specified
        (some value other than DAV:deny-before-grant, described in
        Section 6.2.1), the DAV:allowed-ace element states that only
        one ACE is permitted for each principal, and an ACE describing
        the privileges granted the DAV:all principal must exist in
        every ACL.
   
   
        >> Request <<
   
        PROPFIND /papers/ HTTP/1.1
        Host: www.webdav.org
        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:acl-semantics/>
        </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.webdav.org/papers/</D:href>
            <D:propstat>
              <D:status>HTTP/1.1 200 OK</D:status>
              <D:prop>
                <D:acl-semantics>
                  <D:ace-combination>
                    <D:first-match/>
                  </D:ace-combination>
                  <D:ace-ordering/>
                  <D:allowed-ace>
                    <D:principal-only-one-ace/>
                  </D:allowed-ace>
                  <D:required-principal>
   
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                    <D:all/>
                  </D:required-principal>
                </D:acl-semantics>
              </D:prop>
            </D:propstat>
          <D:response>
        </D:multistatus>
   
   
   5.6 DAV:principal-collection-set
   
        This protected property contains zero, one, or more URLs that
        identify a collection principal. It is expected that
        implementations of this protocol will typically use a
        relatively small number of locations in the URL namespace for
        principal, and collection principals. In cases where this
        assumption holds, the DAV:principal-collection-set property
        will contain a small set of URLs identifying the top of a
        collection hierarchy containing multiple principals and
        collection principals. An access control protocol user agent
        could use the contents of DAV:principal-collection-set to query
        the DAV:displayname property (specified in Section 13.2 of
        [RFC2518]) of all principals on that server, thereby yielding
        human-readable names for each principal that could be displayed
        in a user interface.
   
        <!ELEMENT principal-collection-set (href*)>
   
        Since different servers can control different parts of the URL
        namespace, different resources on the same host MAY have
        different DAV:principal-collection-set values. The collections
        specified in the DAV:principal-collection-set MAY be located on
        different hosts from the resource. The URLs in DAV:principal-
        collection-set SHOULD be http or https scheme URLs. For
        security and scalability reasons, a server MAY report only a
        subset of the entire set of known collection principals, and
        therefore clients should not assume they have retrieved an
        exhaustive listing. Additionally, a server MAY elect to report
        none of the collection principals it knows about, in which case
        the property value would be empty.
   
   5.6.1 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.webdav.org/papers/. The
        property contains the two URLs,
        http://www.webdav.org/_acl/users/ and
        http://www.webdav.org/_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
   
   
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        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.webdav.org
        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:principal-collection-set/>
        </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.webdav.org/papers/</D:href>
            <D:propstat>
              <D:status>HTTP/1.1 200 OK</D:status>
              <D:prop>
                <D:principal-collection-set>
                  <D:href>
                    http://www.webdav.org/_acl/users/
                  </D:href>
                  <D:href>
                    http://www.webdav.org/_acl/groups/
                  </D:href>
                </D:principal-collection-set>
              </D:prop>
            </D:propstat>
          </D:response>
        </D:multistatus>
   
   5.7 Example: PROPFIND to retrieve access control properties
   
        The following example shows how access control information can
        be retrieved by using the PROPFIND method to fetch the values
        of the DAV:owner, DAV:supported-privilege-set, DAV:current-
        user-privilege-set, and DAV:acl properties.
   
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        >> Request <<
   
        PROPFIND /top/container/ HTTP/1.1
        Host: www.foo.org
        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:owner/>
          <D:supported-privilege-set/>
          <D:current-user-privilege-set/>
          <D:acl/>
        </D:propfind>
   
        >> Response <<
   
        HTTP/1.1 207 Multi-Status
        Content-Type: text/xml; charset="utf-8"
        Content-Length: xxx
   
        <?xml version="1.0" encoding="utf-8" ?>
        <D:multistatus
           xmlns:D="DAV:"
           xmlns:A="http://www.webdav.org/acl/"> <D:response>
          <D:href>http://www.foo.org/top/container/</D:href>
          <D:propstat>
          <D:status>HTTP/1.1 200 OK</D:status>
          <D:prop>
            <D:owner>
              <D:href>http://www.foo.org/users/gclemm</D:href>
            </D:owner>
            <D:supported-privilege-set>
              <D:supported-privilege>
                <D:privilege> <D:all/> </D:privilege>
                <D:abstract/>
                <D:description>Any operation</D:description>
                <D:supported-privilege>
                  <D:privilege> <D:read/> </D:privilege>
                  <D:description>Read any object</D:description>
                </D:supported-privilege>
                <D:supported-privilege>
                  <D:privilege> <D:write/> </D:privilege>
                  <D:abstract/>
                  <D:description>Write any object</D:description>
                  <D:supported-privilege>
                    <D:privilege> <A:create/> </D:privilege>
                    <D:description>Create an object</D:description>
                  </D:supported-privilege>
                  <D:supported-privilege>
   
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                    <D:privilege> <A:update/> </D:privilege>
                    <D:description>Update an object</D:description>
                  </D:supported-privilege>
                  <D:supported-privilege>
                    <D:privilege> <A:delete/> </D:privilege>
                    <D:description>Delete an object</D:description>
                  </D:supported-privilege>
                </D:supported-privilege>
                <D:supported-privilege>
                  <D:privilege> <D:read-acl/> </D:privilege>
                  <D:description>Read the ACL</D:description>
                </D:supported-privilege>
                <D:supported-privilege>
                  <D:privilege> <D:write-acl/> </D:privilege>
                  <D:description>Write the ACL</D:description>
                </D:supported-privilege>
              </D:supported-privilege>
            </D:supported-privilege-set>
            <D:current-user-privilege-set>
              <D:privilege> <D:read/> </D:privilege>
              <D:privilege> <D:read-acl/> </D:privilege>
            </D:current-user-privilege-set>
            <D:acl>
              <D:ace>
                <D:principal>
                  <D:href>http://www.foo.org/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.foo.org/groups/marketing/</D:href>
                </D:principal>
                <D:deny>
                  <D:privilege> <D:read/> </D:privilege> </D:deny>
              </D:ace>
              <D:ace>
                <D:principal>
                  <D:property> <D:owner/> </D:property> </D:principal>
                <D:grant>
                  <D:privilege> <D:read-acl/> </D:privilege>
                  <D:privilege> <D:write-acl/> </D:privilege>
                </D:grant>
              </D:ace>
              <D:ace>
                <D:principal> <D:all/> </D:principal>
                <D:grant>
                  <D:privilege> <D:read/> </D:privilege></D:grant>
                <D:inherited>
                  <D:href>http://www.foo.org/top/</D:href>
        </D:inherited>
   
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              </D:ace> </D:acl>
            </D:prop>
          </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:
   
          DAV:all (aggregate, abstract)
              |
            +-- DAV:read
            +-- DAV:write (aggregate, abstract)
                 |
                 +-- http://www.webdav.org/acl/create
                 +-- http://www.webdav.org/acl/update
                 +-- http://www.webdav.org/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.foo.org/users/esedlar is granted the DAV:read,
        DAV:write, and DAV:read-acl privileges.
   
        ACE #2: The principals identified by the URL
        http://www.foo.org/groups/marketing/ are denied the DAV:read
        privilege.  In this example, the principal URL identifies a
        group, which is represented by a collection principal.
   
        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.foo.org/top/, the parent collection of this
        resource.
   
   
   
   
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   6  ACL SEMANTICS
   
        The ACL semantics define how multiple ACEs that match the
        current user are combined, what are the constraints on how ACEs
        can be ordered, and which principals must have an ACE.
   
        <!ELEMENT acl-semantics acl-sem*>
   
        <!ELEMENT acl-sem (ace-combination, ace-ordering, allowed-ace,
        required-principal*)>
   
   6.1 ACE Combination
   
        The DAV:ace-combination element defines how privileges from
        multiple ACEs that match the current user will be combined to
        determine the access privileges for that user.  Multiple ACEs
        may match the same user because the same principal can appear
        in multiple ACEs, because multiple principals can identify the
        same user, and because one principal can be a member of another
        principal.
   
        <!ELEMENT ace-combination
         (first-match | all-grant-before-any-deny | specific-deny-
        overrides-grant)>
   
   6.1.1 DAV:first-match ACE Combination
   
        The ACEs are evaluated in the order in which they appear in the
        ACL.  If the first ACE that matches the current user does not
        grant all the privileges needed for the request, the request
        MUST fail.
   
        <!ELEMENT first-match EMPTY>
   
   6.1.2 DAV:all-grant-before-any-deny ACE Combination
   
        The ACEs are evaluated in the order in which they appear in the
        ACL.  If an evaluated ACE denies a privilege needed for the
        request, the request MUST fail.  If all ACEs have been
        evaluated without the user being granted all privileges needed
        for the request, the request MUST fail.
   
        <!ELEMENT all-grant-before-any-deny EMPTY>
   
   6.1.3 DAV:specific-deny-overrides-grant ACE Combination
   
        All ACEs in the ACL are evaluated.  An "individual ACE" is one
        whose principal identifies the current user.  A "group ACE" is
        one whose principal is a collection that contains a principal
        that identifies the current user.  A privilege is granted if it
        is granted by an individual ACE and not denied by an individual
        ACE, or if it is granted by a group ACE and not denied by an
        individual or group ACE.  A request MUST fail if any of its
        needed privileges are not granted.
   
   
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        <!ELEMENT specific-deny-overrides-grant EMPTY>
   
   6.2 ACE Ordering
   
        The DAV:ace-ordering element defines a constraint on how the
        ACEs can be ordered in the ACL.
   
        <!ELEMENT ace-ordering (deny-before-grant)? >
   
   6.2.1 DAV:deny-before-grant ACE Ordering
   
        This element indicates that all deny ACEs must precede all
        grant ACEs.
   
        <!ELEMENT deny-before-grant EMPTY>
   
   6.3 Allowed ACE
   
        The DAV:allowed-ace XML element specifies constraints on what
        kinds of ACEs are allowed in an ACL.
   
        <!ELEMENT allowed-ace (principal-only-one-ace | grant-only)*>
   
   6.3.1 DAV:principal-only-one-ace ACE Constraint
   
        This element indicates that a principal can appear in only one
        ACE per resource.
   
        <!ELEMENT principal-only-one-ace EMPTY>
   
   6.3.2 DAV:grant-only ACE Constraint
   
        This element indicates that ACEs with deny clauses are not
        allowed.
   
        <!ELEMENT grant-only EMPTY>
   
   6.4 Required Principals
   
        The required principal elements identify which principals must
        have an ACE defined in the ACL.
   
        <!ELEMENT required-principal
          (href | all | authenticated | unauthenticated | property |
        self)>
   
        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>
   
   
   
   
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   7  ACCESS CONTROL AND EXISTING METHODS
   
        This section defines the impact of access control functionality
        on existing methods.
   
   7.1 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.
   
   7.1.1 Example - OPTIONS
   
        >> Request <<
   
          OPTIONS /foo.html HTTP/1.1
          Host: www.webdav.org
          Content-Length: 0
   
        >> Response <<
   
          HTTP/1.1 200 OK
          DAV: 1, 2, access-control
          Allow: OPTIONS, GET, PUT, PROPFIND, PROPPATCH, ACL
   
        In this example, the OPTIONS response indicates that the server
        supports access control and that /foo.html can have its access
        control list modified by the ACL method.
   
   7.2 MOVE
   
        When a resource is moved from one location to another due to a
        MOVE request, the non-inherited ACEs in the DAV:acl property of
        the resource MUST NOT be modified, or the MOVE request fails.
   
   7.3 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).
   
   8  ACCESS CONTROL METHODS
   
   8.1 ACL
   
        The ACL method modifies the access control list (which can be
        read via the DAV:acl property) of a resource.  Specifically,
        the ACL method only permits modification to ACEs that are not
        inherited, and are not protected. An ACL method invocation
        modifies all non-inherited and non-protected ACEs in a
        resource's access control list to exactly match the ACEs
        contained within in the DAV:acl XML element (specified in
        Section 5.4) of the request body. An ACL request body MUST
        contain only one DAV:acl XML element. Unless the non-inherited
   
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        and non-protected ACEs of the DAV:acl property of the resource
        can be updated to be exactly the value specified in the ACL
        request, the ACL request MUST fail.
   
        It is possible that the ACEs visible to the current user in the
        DAV:acl property may only be a portion of the complete set of
        ACEs on that resource. If this is the case, an ACL request only
        modifies the set of ACEs visible to the current user, and does
        not affect any non-visible ACE.
   
        In order to avoid overwriting DAV:acl changes by another
        client, a client SHOULD acquire a WebDAV lock on the resource
        before retrieving the DAV:acl property of a resource that it
        intends on updating.
   
   
   
          Implementation Note: Two common operations are to add or
          remove an ACE from an existing access control list. To
          accomplish this, a client uses the PROPFIND method to
          retrieve the value of the DAV:acl property, then parses the
          returned access control list to remove all inherited and
          protected ACEs (these ACEs are tagged with the DAV:inherited
          and DAV:protected XML elements). In the remaining set of non-
          inherited, non-protected ACEs, the client can add or remove
          one or more ACEs before submitting the final ACE set in the
          request body of the ACL method.
   
   8.1.1 ACL Preconditions
   
        An implementation MAY enforce one or more of the following
        constraints on an ACL request.  If the constraint is violated,
        a 403 (Forbidden) response MUST be returned and the indicated
        XML element MUST be returned as the top level element in an XML
        response body.
   
        <DAV:ace-conflict/>: A conflict exists between two or more ACEs
        submitted in the ACL request.
   
        <DAV:protected-ace-conflict/>: A conflict exists between an ACE
        in the ACL request and a protected ACE on the resource. For
        example, if the resource has a protected ACE granting DAV:write
        to a given principal, then it would be a protected ACE conflict
        if the ACL request submitted an ACE denying DAV:write to the
        same principal.
   
        <DAV:inherited-ace-conflict/>: A conflict exists between an ACE
        in the ACL request and an inherited ACE on the resource. For
        example, if the resource inherits an ACE from its parent
        collection granting DAV:write to a given principal, then it
        would be an inherited ACE conflict if the ACL request submitted
        an ACE denying DAV:write to the same principal. Note that
        reporting of this error will be implementation-dependent.
   
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        Implementations have the choice to either report this error, or
        to 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:too-many-aces/>: An implementation MAY limit the number of
        ACEs in an ACL.  However, ACL-compliant servers MUST support at
        least one ACE granting privileges to a single principal, and
        one ACE granting privileges to a collection principal.
   
        <DAV:deny-before-grant/>: All non-inherited deny ACEs MUST
        precede all non-inherited grant ACEs.
   
        <DAV:principal-only-one-ace/>: For implementations that have
        the DAV:principal-only-one-ace constraint (defined in Section
        6.3.1), this XML element indicates that fulfilling the ACL
        request would result in multiple ACEs for one or more
        principals.
   
        <DAV:grant-only/>: For implementations that have the DAV:grant-
        only constraint (defined in Section 6.3.2), this XML element
        indicates the request contained one or more deny ACEs.
   
        <DAV:required-principal>: One or more required principals (see
        Section 6.4) would not be present in the access control list
        after processing the ACL request. The DAV:required-principal
        XML element MUST contain a list of the missing principal(s),
        following the syntax specified in Section 6.4.
   
   
   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.foo.org/users/esedlar  (i.e.,
        the user "esedlar") read and write privileges, grants the owner
        of the resource read-acl and write-acl privileges, and grants
        everyone read privileges.
   
        >> Request <<
   
        ACL /top/container/ HTTP/1.1
        Host: www.foo.org
        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>
   
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            <D:principal>
              <D:href>http://www.foo.org/users/esedlar</D:href>
            </D:principal>
            <D:grant>
              <D:privilege> <D:read/> </D:privilege>
              <D:privilege> <D:write/> </D:privilege>
            </D:grant>
          </D:ace>
          <D:ace>
            <D:principal>
              <D:property> <D:owner/> </D:property>
            </D:principal>
            <D:grant>
              <D:privilege> <D:read-acl/> </D:privilege>
              <D:privilege> <D:write-acl/> </D:privilege>
            </D:grant>
          </D:ace>
          <D:ace>
            <D:principal> <D:all/> </D:principal>
            <D:grant>
              <D:privilege> <D:read/> </D:privilege>
            </D:grant>
          </D:ace> </D:acl>
   
        >> Response <<
   
        HTTP/1.1 200 OK
   
   8.1.3 Example: ACL method failure due to protected ACE conflict
   
        In the following request, user "fielding", authenticated by
        information in the Authorization header, attempts to deny the
        principal identified by the URL
        http://www.foo.org/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 identified by URL http://www.foo.org/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.foo.org
        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" ?>
   
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        <D:acl xmlns:D="DAV:">
          <D:ace>
            <D:principal>
              <D:href>http://www.foo.org/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" ?>
        <DAV:protected-ace-conflict/>
   
   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.foo.org/top/index.html. This resource has two
        inherited ACEs.
   
        Inherited ACE #1 grants the principal identified by URL
        http://www.foo.org/users/ejw (i.e., the user "ejw")
        http://www.foo.org/privs/write-all and DAV:read-acl privileges.
        On this server, http://www.foo.org/privs/write-all is an
        aggregate privilege containing DAV:write, and DAV:write-acl.
   
        Inherited ACE #2 grants principal DAV:all the DAV:read
        privilege.
   
        The request attempts to set a (non-inherited) ACE, denying the
        principal identified by the URL http://www.foo.org/users/ejw
        (i.e., the user ôejwö) DAV:write permission. This conflicts
        with inherited ACE #1. Note that the decision to report an
        inherited ACE conflict is specific to this server
        implementation. Another server implementation could have
        allowed the new ACE to be set, and then used normal ACE
        evaluation rules to determine whether the new ACE has any
        impact on the privileges available to a principal.
   
        >> Request <<
   
        ACL /top/index.html HTTP/1.1
        Host: www.foo.org
        Content-Type: text/xml; charset="utf-8"
        Content-Length: xxxx
        Authorization: Digest username="ejw",
   
   
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           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.foo.org/privs/">
          <D:ace>
            <D:principal>
              <D:href>http://www.foo.org/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" ?>
        <DAV:inherited-ace-conflict/>
   
   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.foo.org/diamond/engagement-
        ring.gif. The ACL request includes a single, syntactically and
        semantically incorrect ACE, which attempts to grant the
        collection principal identified by the URL
        http://www.foo.org/users/friends/ DAV:read privilege and deny
        the principal identified by URL
        http://www.foo.org/users/ygoland-so (i.e., the user "ygoland-
        so") DAV:read privilege. However, it is illegal to have
        multiple principal elements, as well as both a grant and deny
        element in the same ACE, so the request fails due to poor
        syntax.
   
        >> Request <<
   
        ACL /diamond/engagement-ring.gif HTTP/1.1
        Host: www.foo.org
        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>
   
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              <D:href>http://www.foo.org/users/friends/</D:href>
            </D:principal>
            <D:grant><D:read/></D:grant>
            <D:principal>
              <D:href>http://www.foo.org/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
   
        A REPORT request is an extensible mechanism for obtaining
        information about a resource.  Unlike a resource property,
        which has a single value, the value of a report can depend on
        additional information specified in the REPORT request body and
        in the REPORT request headers.
   
      Marshalling:
   
        The body of a REPORT request specifies which report is being
        requested, as well as any additional information that will be
        used to customize the report.
   
        The request MAY include a Depth header.
   
        The response body for a successful request MUST contain the
        requested report.
   
        If a Depth request header is included, the response MUST be a
        207 Multi-Status.
   
      Postconditions:
   
        The REPORT method MUST NOT change the content or dead
        properties of any resource.
   
        If a Depth request header is included, the request MUST be
        applied separately to the collection itself and to all members
        of the collection that satisfy the Depth value.  The DAV:prop
        element of a DAV:response for a given resource MUST contain the
        requested report for that resource.
   
   
   
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   9.2 DAV:acl-principal-props Report
   
        The DAV:acl-principle-props report returns, for all principals
        in the DAV:acl property that are identified by http(s) URLs,
        the value of the properties specified in the REPORT request
        body. In the case where a principal URL appears multiple times,
        the DAV:acl-principal-props report MUST return the properties
        for that principal only once.
   
      Marshalling
   
        The request body MUST be a DAV:acl-principal-props XML element.
   
        <!ELEMENT acl-principal-props ANY>
        ANY value: a sequence of one or more elements, with at most one
        DAV:prop element.
        prop: see RFC 2518, Section 12.11
   
   
        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).
   
        multistatus: see RFC 2518, Section 12.9
   
        The response body for a successful DAV:acl-principal-props
        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.
   
    9.2.1 Example: DAV:acl-principal-props Report
   
        Resource http;//www.webdav.org/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.webdav.org/people/gstein (the user ôgsteinö) is
        granted DAV:write,  DAV:write-acl, DAV:read-acl privileges.
   
        ACE #3: The collection principal identified by
        http://www.webdav.org/groups/authors/ (the ôauthorsö group) is
        granted DAV:write and DAV:read-acl privileges.
   
        The following example shows a DAV:acl-principal-props report
        requesting the DAV:displayname property. It returns the value
        of DAV:displayname for resources
        http://www.webdav.org/people/gstein and
        http://www.webdav.org/groups/authors/ , but not for DAV:all,
        since this is not an http(s) URL.
   
   
   
   
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        >> Request <<
   
        REPORT /index.html HTTP/1.1
        Host: www.webdav.org
        Content-Type: text/xml; charset="utf-8"
        Content-Length: xxxx
   
        <?xml version="1.0" encoding="utf-8" ?>
        <D:acl-principal-props xmlns:D="DAV:">
          <D:prop>
            <D:displayname/>
          </D:prop>
        </D:acl-principal-props>
   
        >> 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.webdav.org/people/gstein</D:href>
            <D:propstat>
              <D:prop>
                <D:displayname>Greg Stein</D:displayname>
              </D:prop>
              <D:status>HTTP/1.1 200 OK</D:status>
            </D:propstat>
          </D:response>
          <D:response>
            <D:href>http://www.webdav.org/groups/authors/</D:href>
            <D:propstat>
              <D:prop>
                <D:displayname>Site authors</D:displayname>
              </D:prop>
              <D:status>HTTP/1.1 200 OK</D:status>
            </D:propstat>
          </D:response>
        </D:multistatus>
   
   9.3 DAV:principal-match REPORT
   
        The DAV:principal-match REPORT is used to identify all members
        of a collection 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),
        then 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
   
   
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        the resources in a collection hierarchy that are owned by the
        current user.
   
      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
   
   
        The response body for a successful request MUST be a
        DAV:multistatus XML element.
   
        multistatus: see RFC 2518, Section 12.9
   
   
        The response body for a successful DAV:principal-match REPORT
        request MUST contain a DAV:response element for each member of
        the collection that matches the current user. When the
        DAV:principal-property element is used, a match occurs if the
        current user is the same as 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
        collection principal, it matches a child of the collection
        principal if that child (a principal resource) identifies the
        same principal as the current user.
   
        If DAV:prop is specified in the request body, the properties
        specified in the DAV:prop element MUST be reported in the
        DAV:response elements.
   
   9.3.1 Example: DAV:principal-match REPORT
   
        The following example identifies the members of the collection
        identified by the URL http://www.webdav.org/doc/ that are owned
        by the current user. The current user (ôgclemmö) is
        authenticated using Digest authentication.
   
        >> Request <<
   
        REPORT /doc/ HTTP/1.1
        Host: www.webdav.org
        Authorization: Digest username="gclemm",
           realm="gclemm@webdav.org", nonce="...",
           uri="/papers/", response="...", opaque="..."
        Content-Type: text/xml; charset="utf-8"
        Content-Length: xxxx
   
   
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        <?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.webdav.org/doc/foo.html</D:href>
            <D:status>HTTP/1.1 200 OK</D:status>
          </D:response>
          <D:response>
            <D:href>http://www.webdav.org/doc/img/bar.gif</D:href>
            <D:status>HTTP/1.1 200 OK</D:status>
          </D:response>
        </D:multistatus>
   
   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 WebDAV XML Namespace interpretation
        convention, described in Section 23.4 of [RFC2518].
   
   11 INTERNATIONALIZATION CONSIDERATIONS
   
        In this specification, the only human-readable content can be
        found in the description XML element, found within the
        DAV:supported-privilege-set property.  This element contains a
        human-readable description of the capabilities controlled by a
        privilege.  As a result, the description element must be
        capable of representing descriptions in multiple character
        sets.  Since the description element is found within a WebDAV
        property, it is represented on-the-wire as XML [REC-XML], and
        hence can leverage XML's language tagging and character set
        encoding capabilities. Specifically, XML processors must, at
        minimum, 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.
   
        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
   
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        into human-readable text in the user's language and character
        set when displayed to a person.  Only a generic WebDAV property
        display utility would display these values in their raw form to
        a human user.
   
        For error reporting, we follow the convention of HTTP/1.1
        status codes, including with each status code a short, English
        description of the code (e.g., 200 (OK)).  While the
        possibility exists that a poorly crafted user agent would
        display this message to a user, internationalized applications
        will ignore this message, and display an appropriate message in
        the user's language and character set.
   
        Further internationalization considerations for this protocol
        are described in the WebDAV Distributed Authoring protocol
        specification [RFC2518].
   
   12 SECURITY CONSIDERATIONS
   
        Applications and users of this access control protocol should
        be aware of several security considerations, detailed below. In
        addition to the discussion in this document, the security
        considerations detailed in the HTTP/1.1 specification
        [RFC2616], the WebDAV Distributed Authoring Protocol
        specification [RFC2518], and the XML Media Types specification
        [RFC3023] should be considered in a security analysis of this
        protocol.
   
   12.1 Increased Risk of Compromised Users
   
        In the absence of a mechanism for remotely manipulating access
        control lists, if a single user's authentication credentials
        are compromised, only those resources for which the user has
        access permission can be read, modified, moved, or deleted.
        With the introduction of this access control protocol, if a
        single compromised user has the ability to change ACLs for a
        broad range of other users (e.g., a super-user), the number of
        resources that could be altered by a single compromised user
        increases. This risk can be mitigated by limiting the number of
        people who have write-acl privileges across a broad range of
        resources.
   
   12.2 Risks of the DAV:read-acl and DAV:current-user-privilege-set
        Privileges
   
        The ability to read the access privileges (stored in the
        DAV:acl property), or the privileges permitted the currently
        authenticated user (stored in the DAV:current-user-privilege-
        set property) on a resource may seem innocuous, since reading
        an ACL cannot possibly affect the resource's state. However, if
        all resources have world-readable ACLs, it is possible to
        perform an exhaustive search for those resources that have
        inadvertently left themselves in a vulnerable state, such as
        being world-writeable. In particular, the property retrieval
   
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        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
        cuprivset privileges for authenticated principals should be
        carefully analyzed when deploying this protocol. Access to the
        current-user-privilege-set property will involve a tradeoff of
        usability versus security. When the current-user-privilege-set
        is visible, user interfaces are expected to provide enhanced
        information concerning permitted and restricted operations, yet
        this information may also indicate a vulnerability that could
        be exploited. Deployment of this protocol will need to evaluate
        this tradeoff in light of the requirements of the deployment
        environment.
   
   12.3 No Foreknowledge of Initial ACL
   
        In an effort to reduce protocol complexity, this protocol
        specification intentionally does not address the issue of how
        to manage or discover the initial ACL that is placed upon a
        resource when it is created. The only way to discover the
        initial ACL is to create a new resource, then retrieve the
        value of the DAV:acl property. This assumes the principal
        creating the resource also has been granted the DAV:read-acl
        privilege.
   
        As a result, it is possible that a principal could create a
        resource, and then discover that its ACL grants privileges that
        are undesirable. Furthermore, this protocol makes it possible
        (though unlikely) that the creating principal could be unable
        to modify the ACL, or even delete the resource. Even when the
        ACL can be modified, there will be a short period of time when
        the resource exists with the initial ACL before its new ACL can
        be set.
   
        Several factors mitigate this risk. Human principals are often
        aware of the default access permissions in their editing
        environments and take this into account when writing
        information. Furthermore, default privilege policies are
        usually very conservative, limiting the privileges granted by
        the initial ACL.
   
   13 AUTHENTICATION
   
        Authentication mechanisms defined in WebDAV also apply to this
        WebDAV Access Control Protocol, in particular the Basic and
        Digest authentication mechanisms defined in [RFC2617].
   
   
   
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   14 IANA CONSIDERATIONS
   
        This document uses the namespace defined by [RFC2518] for XML
        elements.  All other IANA considerations mentioned in [RFC2518]
        also applicable to WebDAV ACL.
   
   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 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, Gino Basso, Murthy
        Chintalapati, Dennis Hamilton, Laurie Harper, Ron Jacobs, Chris
        Knight, Remy Maucherat, Larry Masinter, Yaron Goland, Lisa
        Dusseault, and Joe Orton. 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
        WebDAV and HTTP protocols upon which this protocol is layered,
        and the invaluable feedback from the WebDAV working group.
   
   
   
   
   
   
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   17 REFERENCES
   
   17.1 Normative References
   
        [RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
        Requirement Levels." RFC 2119, BCP 14, Harvard, March, 1997.
   
        [REC-XML] T. Bray, J. Paoli, C.M. Sperberg-McQueen, "Extensible
        Markup Language (XML)." World Wide Web Consortium
        Recommendation REC-xml-19980210. http://www.w3.org/TR/REC-xml-
        19980210.
   
        [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. U.C. Irvine, Compaq, Xerox,
        Microsoft, MIT/LCS, 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. Northwestern University, Verisign, AbiSource, Agranat,
        Microsoft, Netscape, Open Market, June, 1999.
   
        [RFC2518] Y. Goland, E. Whitehead, A. Faizi, S. R. Carter, D.
        Jensen, "HTTP Extensions for Distributed Authoring -- WEBDAV."
        RFC 2518. Microsoft, U.C. Irvine, Netscape, Novell, February,
        1999.
   
        [RFC2368] P. Hoffman, L. Masinter, J. Zawinski, "The mailto URL
        scheme." RFC 2368. Internet Mail Consortium, Xerox, Netscape,
        July, 1998.
   
        [RFC2255] T. Howes, M. Smith, "The LDAP URL Format." RFC 2255.
        Netscape, December, 1997.
   
        [RFC3023] M. Murata, S. St.Laurent, D. Kohn, "XML Media Types."
        RFC 3023. IBM Tokyo Research Laboratory, simonstl.com, Skymoon
        Ventures, January, 2001.
   
        [UTF-8] F. Yergeau, "UTF-8, a transformation format of Unicode
        and ISO 10646." RFC 2279. Alis Technologies. January, 1998.
   
   17.2 Informational References
   
        [RFC2026] S.Bradner, "The Internet Standards Process û Revision
        3." RFC 2026, BCP 9. Harvard, October, 1996.
   
   18 AUTHORS' ADDRESSES
   
        Geoffrey Clemm
        Rational Software
        20 Maguire Road
        Lexington, MA 02421
        Email: geoffrey.clemm@rational.com
   
   
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        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: esedlar@us.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
   
   
   19 APPENDICIES
   
   19.1 XML Document Type Definition
   
        <!-- Privileges -->
   
        <!ELEMENT read EMPTY>
        <!ELEMENT write EMPTY>
        <!ELEMENT read-acl EMPTY>
        <!ELEMENT read-current-user-privilege-set EMPTY>
        <!ELEMENT write-acl EMPTY>
        <!ELEMENT all EMPTY>
   
   
        <!-- Principal Properties (Section 4) -->
   
        <!ELEMENT is-principal (#PCDATA)>
   
        <!ELEMENT alternate-URL (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*)>
   
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        <!ELEMENT privilege ANY>
        <!ELEMENT abstract EMPTY>
        <!ELEMENT description #PCDATA>
        <!ELEMENT privilege ANY>
   
   
        <!-- DAV:current-user-privilege-set Property (Section 5.3) -->
   
        <!ELEMENT current-user-privilege-set (privilege*)>
   
   
        <!-- DAV:acl Property (Section 5.4) -->
   
        <!ELEMENT acl (ace*)>
   
        <!ELEMENT ace (principal, (grant|deny), protected?,
        inherited?)>
        <!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:principal-collection-set Property (Section 5.6) -->
   
        <!ELEMENT principal-collection-set (href*)>
   
   
        <!-- DAV:acl-semantics Property (Section 6) -->
   
        <!ELEMENT acl-semantics acl-sem*>
        <!ELEMENT acl-sem (ace-combination, ace-ordering, allowed-ace,
        required-principal*)>
   
        <!ELEMENT ace-combination
         (first-match | all-grant-before-any-deny | specific-deny-
        overrides-grant)>
        <!ELEMENT first-match EMPTY>
        <!ELEMENT all-grant-before-any-deny EMPTY>
   
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        <!ELEMENT specific-deny-overrides-grant EMPTY>
   
        <!ELEMENT ace-ordering (deny-before-grant)? >
        <!ELEMENT deny-before-grant EMPTY>
   
        <!ELEMENT allowed-ace (principal-only-one-ace | grant-only)*>
        <!ELEMENT principal-only-one-ace EMPTY>
        <!ELEMENT grant-only EMPTY>
   
        <!ELEMENT required-principal
          (href | all | authenticated | unauthenticated | property |
        self)>
   
   
        <!-- ACL method preconditions (Section 8.1.1) -->
   
   
        <!ELEMENT ace-conflict EMPTY>
        <!ELEMENT protected-ace-conflict EMPTY>
        <!ELEMENT inherited-ace-conflict EMPTY>
        <!ELEMENT too-many-aces EMPTY>
   
   
        <!-- REPORT Method -->
   
        <!ELEMENT acl-principal-props 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>
   
   
   20 NOTE TO RFC EDITOR
   
        *** This section (Section 20) MUST be removed before
        publication as an RFC ***
   
        Section 9.1 defines the REPORT method. The REPORT method is
        also defined in draft-ietf-deltav-versioning-15, in Section
        3.6, using identical text. This was done to avoid making this
        specification dependent on draft-ietf-deltav-versioning.
   
        If draft-ietf-deltav-versioning is published as an RFC before
        this specification, Section 9.1 MUST be removed.
   
   
   
   
   
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