Network Working Group W. Sanchez

Network Working Group W. Sanchez
Request for Comments: 5397 C. Daboo
Category: Standards Track Apple Inc.
December 2008

WebDAV Current Principal Extension

Status of This Memo

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

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Abstract

This specification defines a new WebDAV property that allows clients
to quickly determine the principal corresponding to the current
authenticated user.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . . 2
3. DAV:current-user-principal . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . . 4

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RFC 5397 WebDAV Current Principal December 2008

1. 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].

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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 in Section 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)>


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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: [email protected]
URI: http://www.apple.com/

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RFC 5397 WebDAV Current Principal December 2008

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

EMail: [email protected]
URI: http://www.apple.com/

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