


Network Working Group                                           C. Daboo
Internet-Draft                                                Apple Inc.
Updates: XXXX-CardDAV                                    August 24, 2010
(if approved)
Intended status: Standards Track
Expires: February 25, 2011


                  CardDAV Directory Gateway Extension
                draft-daboo-carddav-directory-gateway-02

Abstract

   This document defines an extension to the vCard Extensions to WebDAV
   (CardDAV) protocol that allows a server to expose a directory as a
   read-only address book collection.

Status of this Memo

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   This Internet-Draft will expire on February 25, 2011.

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Table of Contents

   1.  Introduction and Overview  . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  CARDDAV:directory-gateway Property . . . . . . . . . . . . . .  4
   4.  XML Element Definitions  . . . . . . . . . . . . . . . . . . .  5
     4.1.  CARDDAV:directory  . . . . . . . . . . . . . . . . . . . .  5
   5.  Client Guidelines  . . . . . . . . . . . . . . . . . . . . . .  5
   6.  Server Guidelines  . . . . . . . . . . . . . . . . . . . . . .  6
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   8.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . .  8
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  8
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     10.1. Normative References . . . . . . . . . . . . . . . . . . .  8
     10.2. Informative References . . . . . . . . . . . . . . . . . .  9
   Appendix A.  Change History (to be removed prior to
                publication as an RFC)  . . . . . . . . . . . . . . .  9
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10

































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1.  Introduction and Overview

   The CardDAV [I-D.ietf-vcarddav-carddav] protocol defines a standard
   way of accessing, managing, and sharing contact information based on
   the vCard [RFC2426] format.  Often, in an enterprise or service
   provider environment, a directory of all users hosted on the server
   (or elsewhere) is available (for example via Lightweight Directory
   Access Protocol (LDAP) [RFC4510] or some direct database access).  It
   would be convenient for CardDAV clients if this directory were
   exposed as a "global" address book on the CardDAV server so it could
   be searched in the same way as personal address books are.  This
   specification defines a "directory gateway" feature extension to
   CardDAV to enable this.

   This specification adds one new WebDAV property to principal
   resources that contains the URL to one or more directory gateway
   address book collection resources.  It is important for clients to be
   able to distinguish this address book collection from others because
   there are specific limitations involved in using it as described
   below.  To aid that, this specification defines an XML element that
   can be included as a child element of the DAV:resourcetype property
   of address book collections to identify them as directory gateways.

   Note that this feature is in no way intended to replace full
   directory access - it is meant to simply provide a convenient way for
   CardDAV clients to query contact-related attributes in directory
   records.


2.  Conventions

   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].

   The term "protected" is used in the Conformance field of property
   definitions as defined in Section 15 of [RFC4918].

   This document uses XML DTD fragments ([W3C.REC-xml-20081126], Section
   3.2) as a purely notational convention.  WebDAV request and response
   bodies cannot be validated by a DTD due to the specific extensibility
   rules defined in Section 17 of [RFC4918] and due to the fact that all
   XML elements defined by this specification use the XML namespace name
   "DAV:".  In particular:

   1.  element names use the "DAV:" namespace,





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   2.  element ordering is irrelevant unless explicitly stated,

   3.  extension elements (elements not already defined as valid child
       elements) may be added anywhere, except when explicitly stated
       otherwise,

   4.  extension attributes (attributes not already defined as valid for
       this element) may be added anywhere, except when explicitly
       stated otherwise.

   When XML element types in the namespaces "DAV:" and
   "urn:ietf:params:xml:ns:carddav" are referenced in this document
   outside of the context of an XML fragment, the strings "DAV:" and
   "CARDDAV:" will be prefixed to the element types, respectively.


3.  CARDDAV:directory-gateway Property

   Name:  directory-gateway

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Identifies URLs of CardDAV address book collections acting
      as a directory gateway for the server.

   Protected:  MUST be protected.

   allprop behavior:  SHOULD NOT be returned by a PROPFIND DAV:allprop
      request.

   Description:  The CARDDAV:directory-gateway identifies address book
      collection resources that are directory gateway address books for
      the server.

   Definition:

       <!ELEMENT directory-gateway (DAV:href*)>

   Example:

       <C:directory-gateway xmlns:D="DAV:"
          xmlns:C="urn:ietf:params:xml:ns:carddav">
         <D:href>/directory</D:href>
       </C:directory-gateway>







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4.  XML Element Definitions

4.1.  CARDDAV:directory

   Name:  directory

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Used to indicate that an address book collection is a
      directory gateway.

   Description:  This element appears in the DAV:resourcetype property
      on a address book collection resources that are directory
      gateways.  Clients can use the presence of this element to
      identify directory gateway collections when doing PROPFINDs to
      list collection contents.

   Definition:

   <!ELEMENT directory EMPTY>

   Example:

       <D:resourcetype xmlns:D="DAV:"
          xmlns:C="urn:ietf:params:xml:ns:carddav">
         <D:collection/>
         <C:addressbook/>
         <C:directory/>
       </D:resourcetype>


5.  Client Guidelines

   Clients wishing to make use of directory gateway address books can
   request the CARDDAV:directory-gateway property (Section 3) when
   examining other properties on the principal resource for the user.
   If the property is not present, then the directory gateway feature is
   not supported by the server at that time.

   Clients can also detect the presence of directory gateway address
   book collections by retrieving the DAV:resourcetype property on
   collections that it lists, and look for the presence of the CARDDAV:
   directory element (Section 4.1).

   Since the directory being exposed via a directory gateway address
   book collection could be large, clients SHOULD limit the number of
   results returned in an CARDDAV:addressbook-query REPORT as defined in
   Section 8.6.1 of [I-D.ietf-vcarddav-carddav].



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   Clients MUST treat the directory gateway address book collection as a
   read-only collection, so HTTP methods that modify resource data or
   properties in the address book collection MUST NOT be used.

   Clients SHOULD NOT attempt to cache the entire contents of the
   directory gateway address book collection resource by retrieving all
   resources, or trying to examine all the properties of all resources
   (e.g., via a PROPFIND Depth:1 request).  Instead, CARDDAV:
   addressbook-query REPORTs are used to search for specific address
   book object resources, and CARDDAV:multiget REPORTs and individual
   GET requests can be made to retrieve the actual vCard data for
   address book object resources found via a query.

   When presenting directory gateway collections to the user, clients
   SHOULD use the DAV:displayname property on the corresponding address
   book collections as the name of the directory gateway.  This is
   important in the case where more than one directory gateway is
   available.  Clients MAY also provide descriptive information about
   each directory gateway by examining the CARDDAV:addressbook-
   description property (see Section 6.2.1 of
   [I-D.ietf-vcarddav-carddav]) on the resource.


6.  Server Guidelines

   Servers wishing to expose a directory gateway as an address book
   collection MUST include the CARDDAV:directory-gateway property on all
   principal resources of users expected to use the feature.

   Since the directory being exposed via the directory gateway address
   book collection could be large, servers SHOULD truncate the number of
   results returned in an CARDDAV:addressbook-query REPORT as defined in
   Section 8.6.2 of [I-D.ietf-vcarddav-carddav].  In addition, servers
   SHOULD disallow requests that effectively enumerate the collection
   contents (e.g., PROPFIND Depth:1, trivial CARDDAV:addressbook-query,
   DAV:sync-collection REPORT).

   Servers need to expose the directory information as a set of address
   book object resources in the directory gateway address book
   collection resource.  To do that, a mapping between the directory
   record format and the vCard data has to be applied.  In general, only
   directory record attributes that have a direct equivalent in vCard
   SHOULD be mapped.  It is up to individual implementations to
   determine which attributes to map.  But in all cases servers MUST
   generate valid vCard data as returned to the client.  In addition, as
   required by CardDAV, the UID vCard property MUST be present in the
   vCard data, and this value MUST be persistent from query to query for
   the same directory record.



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   Multiple directory sources could be available to the server.  The
   server MAY use a single directory gateway resource to aggregate
   results from each directory source.  When doing so care is needed
   when dealing with potential records that refer to the same entity.
   Servers MAY suppress any duplicates that they are able to determine
   themselves.  Alternatively, multiple directory sources can be exposed
   as separate directory gateway resources.

   For any directory source, a server MAY expose multiple directory
   gateway resources where each represents a different query "scope" for
   the directory.  Different scopes MAY be offered to different
   principals on the server.  For example, the server might expose an
   entire company directory for searching as the resource "/directory-
   all" to all principals, but then provide "/directory-department-XYZ"
   as another directory gateway that has a search scope that implicitly
   limits the search results to just the "XYZ" department.  Users in
   that department would then have a CARDDAV:directory-gateway property
   on their principal resource that included the "/directory-department-
   XYZ" resource.  Users in other departments would have corresponding
   directory gateway resources available to them.

   Records in a directory can include data for more than just people,
   e.g, resources such as rooms or projectors, groups, computer systems
   etc.  It is up to individual implementations to determine the most
   appropriate "scope" for the data returned via the directory gateway
   by filtering the appropriate record types.  As above, servers could
   choose to expose people and resources under different directory
   gateway resources by implicitly limiting the search "scope" for each
   of those.

   Servers MAY apply implementation defined access rules to determine,
   on a per-user basis, what records are returned to a particularly user
   and the content of those records exposed via vCard data.  This per-
   user behavior is in addition to the general security requirements
   detailed below.

   When multiple directory gateway collections are present, servers
   SHOULD provide a DAV:displayname property on each that disambiguates
   them.  Servers MAY include a CARDDAV:addressbook-description property
   (see Section 6.2.1 of [I-D.ietf-vcarddav-carddav]) on each directory
   gateway resource to provide a description of the directory and any
   search "scope" that might be used, or any other useful information
   for users.


7.  Security Considerations

   Servers MUST ensure that client requests against the directory



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   gateway address book collection cannot use excessive resources (CPU,
   memory, network bandwidth etc), given that the directory could be
   large.

   Servers MUST take care not to expose sensitive directory record
   attributes in the vCard data via the directory gateway address book.
   In general only those properties that have direct correspondence in
   vCard SHOULD be exposed.

   Servers need to determine whether it is appropriate for the directory
   information to be available via CardDAV to unauthenticated users.  If
   not, servers MUST ensure that unauthenticated users do not have
   access to the directory gateway address book object resource and its
   contents.  If unauthenticated access is allowed, servers MAY choose
   to limit the set of vCard properties that are searchable or returned
   in the address book object resources when unauthenticated requests
   are made.


8.  IANA Consideration

   This document does not require any actions on the part of IANA.


9.  Acknowledgments


10.  References

10.1.  Normative References

   [I-D.ietf-vcarddav-carddav]
              Daboo, C., "vCard Extensions to WebDAV (CardDAV)",
              draft-ietf-vcarddav-carddav-10 (work in progress),
              November 2009.

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

   [RFC2426]  Dawson, F. and T. Howes, "vCard MIME Directory Profile",
              RFC 2426, September 1998.

   [RFC4918]  Dusseault, L., "HTTP Extensions for Web Distributed
              Authoring and Versioning (WebDAV)", RFC 4918, June 2007.

   [W3C.REC-xml-20081126]
              Paoli, J., Yergeau, F., Bray, T., Sperberg-McQueen, C.,
              and E. Maler, "Extensible Markup Language (XML) 1.0 (Fifth



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              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126>.

10.2.  Informative References

   [RFC4510]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP): Technical Specification Road Map", RFC 4510,
              June 2006.


Appendix A.  Change History (to be removed prior to publication as an
             RFC)

   Changes in -02

   1.  Added CARDDAV:directory element for use in DAV:resourcetype

   2.  Allow CARDDAV:directory-gateway to be multi-valued

   3.  Explain how a server could implicit "scope" queries on different
       directory gateway resources

   Changes in -01

   1.  Remove duplicated text in a couple of sections

   2.  Add example of LDAP/generic database as possible directory
       "sources"

   3.  Add text to explain why the client needs to treat this as special
       and thus the need for a property

   4.  Added text to server guidelines indicating requirements for
       handling vCard UID properties

   5.  Added text to server guidelines explain that different record
       "types" may exist in the directory and the server is free to
       filter those as appropriate

   6.  Added text to server guidelines indicating that server are free
       to aggregate directory records from multiple sources

   7.  Added text to server guidelines indicating that servers are free
       to apply implementation defined access control to the returned
       data on a per-user basis





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Author's Address

   Cyrus Daboo
   Apple Inc.
   1 Infinite Loop
   Cupertino, CA  95014
   USA

   Email: cyrus@daboo.name
   URI:   http://www.apple.com/









































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