SIMPLE J. Rosenberg
Internet-Draft dynamicsoft
Expires: April 26, 2004 October 27, 2003
Extensible Markup Language (XML) Configuration Access Protocol (XCAP)
Usages for Setting Presence Authorization
draft-ietf-simple-xcap-auth-usage-01
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Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes two usages of the Extensible Markup Language
(XML) Configuration Access Protocol (XCAP) that allow a client to
provide authorization decisions regarding watchers of their presence.
The first of these usages, called permission-statements, contains
statements about what permissions are to be granted to watchers of
presence. The second usage, called supported-permissions, allows a
client to determine what permissions are understood by the provider.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . 3
2. Structuring Presence Authorization . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . 5
4. Permission Statements . . . . . . . . . . . . . . . . . 6
4.1 Application Unique ID . . . . . . . . . . . . . . . . . 6
4.2 Structure of Permission Statements . . . . . . . . . . . 6
4.2.1 Applying Statements to Watchers . . . . . . . . . . . . 6
4.2.2 Specifying Permissions . . . . . . . . . . . . . . . . . 8
4.2.2.1 Acceptance Permissions . . . . . . . . . . . . . . . . . 8
4.2.2.2 Content Permissions . . . . . . . . . . . . . . . . . . 10
4.2.2.2.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . 11
4.3 Additional Constraints . . . . . . . . . . . . . . . . . 12
4.4 Naming Conventions . . . . . . . . . . . . . . . . . . . 12
4.5 Authorization Policies . . . . . . . . . . . . . . . . . 12
4.6 XML Schema . . . . . . . . . . . . . . . . . . . . . . . 13
5. Supported Permissions . . . . . . . . . . . . . . . . . 14
5.1 Application Unique ID . . . . . . . . . . . . . . . . . 14
5.2 Structure of Supported Permissions . . . . . . . . . . . 14
5.3 Naming Conventions . . . . . . . . . . . . . . . . . . . 15
5.4 Authorization Policies . . . . . . . . . . . . . . . . . 15
5.5 XML Schema . . . . . . . . . . . . . . . . . . . . . . . 16
5.6 Example Document . . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . 18
6.1 XCAP Application Usage IDs . . . . . . . . . . . . . . . 18
6.1.1 Permission Statements . . . . . . . . . . . . . . . . . 18
6.1.2 Supported Permissions . . . . . . . . . . . . . . . . . 18
6.2 URN Sub-Namespace Registrations . . . . . . . . . . . . 18
6.2.1 urn:ietf:params:xml:ns:permission-statements . . . . . . 18
6.2.2 urn:ietf:params:xml:ns:supported-permissions . . . . . . 19
6.3 XML Schema Registrations . . . . . . . . . . . . . . . . 20
6.3.1 Permissions Statements . . . . . . . . . . . . . . . . . 20
6.3.2 Supported Permissions . . . . . . . . . . . . . . . . . 20
Normative References . . . . . . . . . . . . . . . . . . 21
Informative References . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . 22
Intellectual Property and Copyright Statements . . . . . 23
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1. Introduction
The Session Initiation Protocol (SIP) for Instant Messaging and
Presence (SIMPLE) specifications allow a user, called a watcher, to
subscribe to another user, called a presentity [13], in order to
learn their presence information [14]. This subscription is handed by
a presence agent. In order to process the subscription, the presence
agent must make a determination about whether the subscription is
authorized. This authorization decision includes whether or not to
accept the subscription, but also includes decisions about when the
watcher should receive notifications, and when it does receive them,
what the content of those notifications should be.
Typically, the authorization decision will be a combination of the
authorization policies of the provider, combined with the
authorization policices of the presentity. In order for the PA to
compute the final authorization decision, it needs access to the
presentity's authorization policies.
In order to provide this access, the XML Configuration Access
Protocol (XCAP) [2] is used. XCAP allows a client to manipulate XML
documents stored on a server. Those XML documents represent per-user
provisioning data on how an application should operate. XCAP has the
notion of an application usage, which is a definition of the XML
schema used by a particular application, along with other relevant
information. Each application usage is given a unique application
usage ID (AUID) which identifies it. This specification makes use of
three application usages.
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2. Structuring Presence Authorization
This specification defines three application usages (each with their
own XML schema) that, put together, present a comprehensive solution
for allowing clients to specify authorization policies that a PA can
use when processing a subscription. The first of these application
usages has the AUID of permission-statements. This usage allows a
client to make statements about which permissions are granted to
which watchers. Each statement contains a definition of the watchers
to whom it applies, and then contains a list of permissions which are
granted to those watchers. The concept of a permission is central to
this specification. A permission is an atomic statement of consent. A
permission can indicate a condition under which a subscription is
accepted or rejected, a condition under which a notification is or is
not sent, or a piece of information which is revealed in a presence
document. The overall authorization for a watcher is represented by
the union of the permissions granted to that watcher.
This specification contains a basic set of primitive permissions. It
is anticipated that new ones will be standardized in the future. It
is also anticipated that vendors will define proprietary permissions.
In order for a client to connect to a server, and achieve
interoperability, it is neccesary for the client to know what
permissions are supported by the server. The second application
usage, supported-permissions, allows a client to read the list of
permissions understood by the server.
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3. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant implementations.
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4. Permission Statements
4.1 Application Unique ID
XCAP requires application usages to define a unique application usage
ID (AUID) in either the IETF tree or a vendor tree. This
specification defines the "permission-statements" AUID within the
IETF tree, via the IANA registration in Section 6.
4.2 Structure of Permission Statements
A permission statement is an XML [3] document that MUST be
well-formed and SHOULD be valid. Permission statement documents MUST
be based on XML 1.0 and MUST be encoded using UTF-8. This
specification makes use of XML namespaces for identifying permission
statement documents and document fragments. The namespace URI for
elements defined for this purpose is a URN [5], using the namespace
identifier 'ietf' defined by [7] and extended by [11]. This URN is:
urn:ietf:params:xml:ns:permission-statements
A permission statement document begins with the root element tag
"permission-statements". It consists of any number of "statement"
elements. Each statement element defines a set of permissions and
identifies to whom they are granted.
Each "statement" element has a single attribute:
id: This is a string which serves as a way to uniquely identify
statements in the document. The attribute MUST be unique amongst
all statement elements in the document. This attribute is
mandatory.
Each statement is composed of a single "applies-to" element and a
single "permissions" element. The "permissions" element is composed
of one or more elements that grant permissions.
4.2.1 Applying Statements to Watchers
The "applies-to" element defines the set of watchers to whom the
statement applies. It contains one or more "uri" elements, "domain"
elements, "on-list" elements or a single "any" element, followed by
any number of "except" elements. The "uri" element identifies a
single watcher by specifying its URI. The "domain" element says that
the statement applies to all watchers from the specified domain. The
"on-list" element says that the statement applies to all users on the
specified presence list [17], identified with an HTTP URI that points
to the list. Finally, the "any" element says that the statement
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applies to all watchers. Additional elements can be added that
express other ways of identifying the watchers to whom the statement
applies. When unioned together, the result of the "uri", "domain",
"on-list" and "any" elements define a set of users to whom the
permission statement applies. This list is reduced in size by the
"except" element, which removes a user or domain from the set. The
"except" element contains instances of the "uri", "domain" and
"on-list" elements, which specify the users, domains, lists to be
removed from the set.
The "uri", "domain", "on-list", and "any" elements all have the
following attributes:
id: This is a string which serves as a way to uniquely identify an
instance of this element within the enclosing "applies-to"
element. The attribute MUST be unique amongst all elements of the
same name within the enclosing "applies-to" element. This
attribute is mandatory.
display-name: This is a string that contains a display name, suitable
for rendering to a human user, the identity of the user or domain
implied by the element. This attribute is optional.
lang: This attribute identifies the language used to represent the
display name. It is imported from the XML namespace. This
attribute is optional.
When a subscription arrives at the PA, the PA performs an
authentication operation to determine the identity of the watcher. It
then uses the "applies-to" element in each statement within the
presentity's document, and determines the set of statements that
apply to the watcher. It is possible that multiple statements can
match a single subscription. In that case, the union of the
permissions across those statements is applied to the subscription.
It is also possible that none of the statements match, in which case
the subscription is considered "pending".
For example, the following XML fragment includes two statements, one
that applies to the user joe@example.com, and another that applies to
example.com. When Joe subscribes, both statements match. Therefore,
he is granted the union of the permissions across the two statements.
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See RFCXXXX.
END 6.2.2 urn:ietf:params:xml:ns:supported-permissions URI: The URI for this namespace is urn:ietf:params:xml:ns:supported-permissions. Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org), Jonathan Rosenberg (jdrosen@jdrosen.net). XML: BEGINSee RFCXXXX.
END Rosenberg Expires April 26, 2004 [Page 19] Internet-Draft XCAP Usage for Authorization October 2003 6.3 XML Schema Registrations This section registers three XML schemas as per the procedures in [11]. 6.3.1 Permissions Statements URI: please assign. Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org), Jonathan Rosenberg (jdrosen@jdrosen.net). The XML for this schema can be found as the sole content of Section 4.6. 6.3.2 Supported Permissions URI: please assign. Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org), Jonathan Rosenberg (jdrosen@jdrosen.net). The XML for this schema can be found as the sole content of Section 5.5. Rosenberg Expires April 26, 2004 [Page 20] Internet-Draft XCAP Usage for Authorization October 2003 Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Rosenberg, J., "The Extensible Markup Language (XML) Configuration Access Protocol (XCAP)", draft-ietf-simple-xcap-00 (work in progress), June 2003. [3] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C REC REC-xml-20001006, October 2000. [4] Clark, J. and S. DeRose, "XML Path Language (XPath) Version 1.0", W3C REC REC-xpath-19991116, November 1999. [5] Moats, R., "URN Syntax", RFC 2141, May 1997. [6] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC 3023, January 2001. [7] Moats, R., "A URN Namespace for IETF Documents", RFC 2648, August 1999. [8] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A. and L. Stewart, "HTTP Authentication: Basic and Digest Access Authentication", RFC 2617, June 1999. [9] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [10] Ramsdell, B., "S/MIME Version 3 Message Specification", RFC 2633, June 1999. [11] Mealling, M., "The IETF XML Registry", draft-mealling-iana-xmlns-registry-05 (work in progress), June 2003. [12] Schulzrinne, H., "RPID -- Rich Presence Information Data Format", draft-ietf-simple-rpid-00 (work in progress), July 2003. Rosenberg Expires April 26, 2004 [Page 21] Internet-Draft XCAP Usage for Authorization October 2003 Informative References [13] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. [14] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work in progress), January 2003. [15] Sugano, H. and S. Fujimoto, "Presence Information Data Format (PIDF)", draft-ietf-impp-cpim-pidf-08 (work in progress), May 2003. [16] Jennings, C., Peterson, J. and M. Watson, "Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted Networks", RFC 3325, November 2002. [17] Rosenberg, J., "An Extensible Markup Language (XML) Configuration Access Protocol (XCAP) Usage for Presence Lists", draft-ietf-simple-xcap-list-usage-00 (work in progress), June 2003. Author's Address Jonathan Rosenberg dynamicsoft 600 Lanidex Plaza Parsippany, NJ 07052 US Phone: +1 973 952-5000 EMail: jdrosen@dynamicsoft.com URI: http://www.jdrosen.net Rosenberg Expires April 26, 2004 [Page 22] Internet-Draft XCAP Usage for Authorization October 2003 Intellectual Property Statement 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 of the 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. 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