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Network Working Group                                         W. SanchezRequest for Comments: 5397                                      C. DabooCategory: Standards Track                                     Apple Inc.                                                           December 2008WebDAV Current Principal ExtensionStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (c) 2008 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.Abstract   This specification defines a new WebDAV property that allows clients   to quickly determine the principal corresponding to the current   authenticated user.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions Used in This Document . . . . . . . . . . . . . . .23.  DAV:current-user-principal  . . . . . . . . . . . . . . . . . .34.  Security Considerations . . . . . . . . . . . . . . . . . . . .45.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .46.  Normative References  . . . . . . . . . . . . . . . . . . . . .4Sanchez & Daboo              Standards Track                    [Page 1]

RFC 5397                WebDAV Current Principal           December 20081.  Introduction   WebDAV [RFC4918] is an extension to HTTP [RFC2616] to support   improved document authoring capabilities.  The WebDAV Access Control   Protocol ("WebDAV ACL") [RFC3744] extension adds access control   capabilities to WebDAV.  It introduces the concept of a "principal"   resource, which is used to represent information about authenticated   entities on the system.   Some clients have a need to determine which [RFC3744] principal a   server is associating with the currently authenticated HTTP user.   While [RFC3744] defines a DAV:current-user-privilege-set property for   retrieving the privileges granted to that principal, there is no   recommended way to identify the principal in question, which is   necessary to perform other useful operations.  For example, a client   may wish to determine which groups the current user is a member of,   or modify a property of the principal resource associated with the   current user.   The DAV:principal-match REPORT provides some useful functionality,   but there are common situations where the results from that query can   be ambiguous.  For example, not only is an individual user principal   returned, but also every group principal that the user is a member   of, and there is no clear way to distinguish which is which.   This specification proposes an extension to WebDAV ACL that adds a   DAV:current-user-principal property to resources under access control   on the server.  This property provides a URL to a principal resource   corresponding to the currently authenticated user.  This allows a   client to "bootstrap" itself by performing additional queries on the   principal resource to obtain additional information from that   resource, which is the purpose of this extension.  Note that while it   is possible for multiple URLs to refer to the same principal   resource, or for multiple principal resources to correspond to a   single principal, this specification only allows for a single http(s)   URL in the DAV:current-user-principal property.  If a client wishes   to obtain alternate URLs for the principal, it can query the   principal resource for this information; it is not the purpose of   this extension to provide a complete list of such URLs, but simply to   provide a means to locate a resource which contains that (and other)   information.2.  Conventions Used in This Document   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].Sanchez & Daboo              Standards Track                    [Page 2]

RFC 5397                WebDAV Current Principal           December 2008   When XML element types in the namespace "DAV:" are referenced in this   document outside of the context of an XML fragment, the string "DAV:"   will be prefixed to the element type names.   Processing of XML by clients and servers MUST follow the rules   defined inSection 17 of WebDAV [RFC4918].   Some of the declarations refer to XML elements defined by WebDAV   [RFC4918].3.  DAV:current-user-principal   Name:  current-user-principal   Namespace:  DAV:   Purpose:  Indicates a URL for the currently authenticated user's      principal resource on the server.   Value:  A single DAV:href or DAV:unauthenticated element.   Protected:  This property is computed on a per-request basis, and      therefore is protected.   Description:  The DAV:current-user-principal property contains either      a DAV:href or DAV:unauthenticated XML element.  The DAV:href      element contains a URL to a principal resource corresponding to      the currently authenticated user.  That URL MUST be one of the      URLs in the DAV:principal-URL or DAV:alternate-URI-set properties      defined on the principal resource and MUST be an http(s) scheme      URL.  When authentication has not been done or has failed, this      property MUST contain the DAV:unauthenticated pseudo-principal.      In some cases, there may be multiple principal resources      corresponding to the same authenticated principal.  In that case,      the server is free to choose any one of the principal resource      URIs for the value of the DAV:current-user-principal property.      However, servers SHOULD be consistent and use the same principal      resource URI for each authenticated principal.   COPY/MOVE behavior:  This property is computed on a per-request      basis, and is thus never copied or moved.   Definition:      <!ELEMENT current-user-principal (unauthenticated | href)>      <!-- href value: a URL to a principal resource -->Sanchez & Daboo              Standards Track                    [Page 3]

RFC 5397                WebDAV Current Principal           December 2008   Example:      <D:current-user-principal xmlns:D="DAV:">        <D:href>/principals/users/cdaboo</D:href>      </D:current-user-principal>4.  Security Considerations   This specification does not introduce any additional security issues   beyond those defined for HTTP [RFC2616], WebDAV [RFC4918], and WebDAV   ACL [RFC3744].5.  Acknowledgments   This specification is based on discussions that took place within the   Calendaring and Scheduling Consortium's CalDAV Technical Committee.   The authors thank the participants of that group for their input.   The authors thank Julian Reschke for his valuable input via the   WebDAV working group mailing list.6.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext              Transfer Protocol -- HTTP/1.1",RFC 2616, June 1999.   [RFC3744]  Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web              Distributed Authoring and Versioning (WebDAV)              Access Control Protocol",RFC 3744, May 2004.   [RFC4918]  Dusseault, L., "HTTP Extensions for Web Distributed              Authoring and Versioning (WebDAV)",RFC 4918, June 2007.Authors' Addresses   Wilfredo Sanchez   Apple Inc.   1 Infinite Loop   Cupertino, CA  95014   USA   EMail: wsanchez@wsanchez.net   URI:http://www.apple.com/Sanchez & Daboo              Standards Track                    [Page 4]

RFC 5397                WebDAV Current Principal           December 2008   Cyrus Daboo   Apple Inc.   1 Infinite Loop   Cupertino, CA  95014   USA   EMail: cyrus@daboo.name   URI:http://www.apple.com/Sanchez & Daboo              Standards Track                    [Page 5]