SIMPLE J. Rosenberg
Internet-Draft dynamicsoft
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Presence Authorization Rules
draft-rosenberg-simple-rules-00
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
Authorization is a key function in presence systems. Authorization
policies, also known as authorization rules, specify what presence
information can be given to which watchers, and when. This
specification defines an Extensible Markup Language (XML) document
format for expressing presence authorization rules. Such a document
can be manipulated by clients using the XML Configuration Access
Protocol (XCAP), although other techniques are permitted.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Structure of Permission Statements . . . . . . . . . . . . . 5
3.1 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1 Identity . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.2 Anonymous . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Actions . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2.1 Accept Subscription . . . . . . . . . . . . . . . . . . . . 6
3.2.2 Provide Presence . . . . . . . . . . . . . . . . . . . . . . 6
3.3 Transformations . . . . . . . . . . . . . . . . . . . . . . 6
3.3.1 Show Namespace . . . . . . . . . . . . . . . . . . . . . . . 7
3.3.2 Show Tuple . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3.3 Show Element . . . . . . . . . . . . . . . . . . . . . . . . 8
4. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Example Document . . . . . . . . . . . . . . . . . . . . . . 11
6. XCAP Usage . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1 Application Unique ID . . . . . . . . . . . . . . . . . . . 12
6.2 Structure of Permission Statements . . . . . . . . . . . . . 12
6.3 Additional Constraints . . . . . . . . . . . . . . . . . . . 12
6.4 Naming Conventions . . . . . . . . . . . . . . . . . . . . . 12
6.5 Authorization Policies . . . . . . . . . . . . . . . . . . . 12
6.6 XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 14
8.1 XCAP Application Usage ID . . . . . . . . . . . . . . . . . 14
8.2 URN Sub-Namespace Registration . . . . . . . . . . . . . . . 14
8.3 XML Schema Registrations . . . . . . . . . . . . . . . . . . 15
Normative References . . . . . . . . . . . . . . . . . . . . 16
Informative References . . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . 19
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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 [15], in order to
learn their presence information [17]. 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 policies of the presentity. In order for the PA to
compute the final authorization decision, it needs access to the
presentity's authorization policies.
[10] specifies a framework for representing such authorization
policies, and is applicable to systems such as geo-location and
presence. In that framework, an authorization document is a sequence
of rule elements. Each rule element contains a conditions element, an
actions element, and a transformations element. The conditions
element specifies under what conditions the rule is to be applied to
a subscription request. The actions element tells the server what
actions to take against the request. The transformations element
indicates how the presence data is to be manipulated before being
presented to that watcher. [10] identifies a small number of specific
conditions, actions and permissions common to presence and location
services, and leaves it to other specifications, such as this one, to
fill in usage specific details.
These documents can be manipulated by clients using several means.
One such mechanism is the XML Configuration Access Protocol (XCAP)
[2]. This specification defines the details necessary for using XCAP
to manage presence authorization documents.
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2. 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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3. Structure of Permission Statements
A permission statement is an XML document, formatted according to the
schema defined in [10]. As described in [10], this document is
composed of three parts - conditions, actions, and transformations.
Each action or transformation, which is also called an attribute, has
the property of being a positive grant of information to the watcher.
As a result, there is a well-defined mechanism for combining actions
and transformations obtained from several sources. This mechanism is
privacy safe, since the lack of any action or transformation can only
result in less information being presented to a watcher.
This section defines the new conditions, actions and transformations
defined by this specification.
3.1 Conditions
3.1.1 Identity
Although the "identity" element is defined in [10], that
specification indicates that the interpretation of the "uri" element
depends on the specific protocol in use and its authentication
mechanisms. This sub-section defines that interpretation for systems
based on [17] [[NOTE: "uri" is a bad choice of name for this element,
since its not a URI. That will be corrected in a subsequent revision
of the common policy document.]]
For requests that are authenticated using SIP [9] digest
authentication [8], the user part of the URI is matched against the
username attribute in the Authorization request header field. The
domain part of the URI is matched against the realm attribute in the
Authorization request header field.
For requests that are authenticated using [18], the username and
domain part of the URI are matched against the user and host parts of
the SIP URI in the P-Asserted-Identity header field.
For requests that are authenticated using [11], the username and
domain part of the URI are matched against the user and host parts of
the SIP URI in the From header field of the Asserted Identity Body
[12].
3.1.2 Anonymous
The "anonymous" element, which is a boolean type, indicates whether
or not the request was authenticated using the "anonymous" username
defined in RFC 3261. It allows for the presentity to specify policies
based on whether or not the requestor was anonymous.
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3.2 Actions
The "confirmation" element specified in [10] applies to presence
systems. When TRUE, it implies that the subscription is placed in the
pending state. Confirmation is provided by modifying the rules to
accept the subscription.
3.2.1 Accept Subscription
The "accept-subscription" element represents a boolean action. If
TRUE, it means that the subscription is to be accepted. If FALSE, it
means that the subscription is to be rejected. If this element is
undefined (i.e., not present in the any matching rule), it has a
value of FALSE and therefore causes the subscription to be blocked.
NOTE WELL: Placing a value of FALSE for this element does not
guarantee that a subscription is denied! If any matching rule has
a value of TRUE for "accept-subscription", the subscription will
be granted due to the combining rules defined in [10].
3.2.2 Provide Presence
The "provide-presence" element is used to implement the "polite
blocking" feature defined in RFC 2779 [16]. The element represents a
boolean data type. When TRUE, it means that actual presence data
(subject to any transformations present in the rules) is given to the
watcher. If FALSE, it means that the subscription is to be
politely-blocked. This implies that the subscription is accepted, but
inaccurate presence data is provided to the watcher. The specific
mechanism for generating inaccurate presence data is at the
discretion of the implementation. Providing a single tuple [3] with a
basic status of closed represents one reasonable choice.
This action only applies if subscription was accepted as a result of
any "accept-subscription" permissions in matching rules.
If this element is not present in any matching rules, it takes on the
default value of FALSE. This means that, by default, a user is
politely blocked if their subscription is accepted. Actual presence
information must be explicitly granted through a "provide-presence"
action.
3.3 Transformations
Each of the sections below defines a particular transformation that
is applied to the presence document before distribution. Each of
these transformations is applied to the document independently of any
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of the others, and the order of application is irrelevant. Each
transformation filters the presence document based on a particular
"axis" - removing tuples by class, elements by namespace, and
elements by qualified name. If such a transformation results in an
invalid or empty presence document, then no document is sent to the
watcher.
Because a particular component of the presence document can be
selected by multiple axes, and because the default is to remove
information, it may be necessary to include several different
transformations in order to include one specific element.
3.3.1 Show Namespace
This element, "show-namespace" is a "set" data type. The content of
the element is either the element "all-ns", which is defined as the
set of all namespaces, or else is a series of "ns" elements, each of
which identifies a specific namespace that is in the set. Any
namespaces identified by this element remain in the document when it
is distributed to a watcher. Elements in the document from namespaces
not in the set are removed.
The default value for this element when not present is
"urn:ietf:params:xml:ns:pidf", which is the namespace identified in
[3]. As a result, if this element is omitted, the result is the
namespace for the basic presence document.
If the "show-namespace" element is present, it SHOULD contain
"urn:ietf:params:xml:ns:pidf" as a member (either explicitly or
through the "all-ns" element). If not, the filtering operation will
result in an invalid presence document, and based on the rules above,
no document will be passed to watchers.
3.3.2 Show Tuple
This element, "show-tuple", is a "set" data type. It identifies the
set of tuples, identified by value of the "class" element [13], that
are passed to the watcher. The content of this element is either the
element "all-tuples", which implies the set of all tuples from the
unfiltered presence document, else is a series of "class" elements.
Each "class" element contains a string that identifies a specific
class to be included in the presence document. If a tuple contains
the class element, and that class is not present in the set, that
tuple is removed from the document. If a tuple does not contain a
class element, it is not subject to filtration by the "show-tuple"
transformation.
The default value of this element is NULL, which corresponds to the
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empty set. As a result, if no matching rules contain a "show-tuple"
element, all tuples containing a class element would be removed from
the presence document.
3.3.3 Show Element
This element, "show-element", is a "set" data type. It identifies the
set of XML elements, identified by qualified element name, which are
to be passed to a watcher in the presence document. The content of
this element is either "all-elements", which implies the set of all
elements from the unfiltered presence document, "basic-elements",
which implies the set of elements defined in [3], and/or a series of
"el" elements. Each "el" element contains a string that identifies an
XML element, by qualified element name. Any XML element in a presence
document not contained in this set is removed from the document.
The default value of this element is "basic-elements", which contains
the values "presence", "tuple", "note", "status", "timestamp",
"contact", and "basic" from the namespace
"urn:ietf:params:xml:ns:pidf". These correspond to the elements
defined in the PIDF specification. As a result, if no matching rules
contain the "show-element" transformation, only the basic presence
information containined in [3] will be provided to watchers.
If the "show-element" transformation is present, it SHOULD contain
sufficient elements to result in a presence document compliant to the
schema defined in [3]. This includes at least the "presence" element.
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4. XML Schema
See RFCXXXX.
END Rosenberg Expires August 9, 2004 [Page 14] Internet-Draft Presence Authorization February 2004 8.3 XML Schema Registrations This section registers an XML schema per the procedures in [14]. 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. Rosenberg Expires August 9, 2004 [Page 15] Internet-Draft Presence Authorization February 2004 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-01 (work in progress), October 2003. [3] Sugano, H. and S. Fujimoto, "Presence Information Data Format (PIDF)", draft-ietf-impp-cpim-pidf-08 (work in progress), May 2003. [4] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C FirstEdition REC-xml-20001006, October 2000. [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] Schulzrinne, H., Morris, J., Tschofenig, H., Cuellar, J., Polk, J. and J. Rosenberg, "Common Policy", draft-ietf-geopriv-common-policy-00 (work in progress), February 2004. [11] Peterson, J., "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", draft-ietf-sip-identity-01 (work in progress), March 2003. [12] Peterson, J., "SIP Authenticated Identity Body (AIB) Format", draft-ietf-sip-authid-body-02 (work in progress), July 2003. [13] Schulzrinne, H., "RPID -- Rich Presence Information Data Format", draft-ietf-simple-rpid-00 (work in progress), July 2003. Rosenberg Expires August 9, 2004 [Page 16] Internet-Draft Presence Authorization February 2004 [14] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. Rosenberg Expires August 9, 2004 [Page 17] Internet-Draft Presence Authorization February 2004 Informative References [15] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. [16] Day, M., Aggarwal, S., Mohr, G. and J. Vincent, "Instant Messaging / Presence Protocol Requirements", RFC 2779, February 2000. [17] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work in progress), January 2003. [18] 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. Author's Address Jonathan Rosenberg dynamicsoft 600 Lanidex Plaza Parsippany, NJ 07054 US Phone: +1 973 952-5000 EMail: jdrosen@dynamicsoft.com URI: http://www.jdrosen.net Rosenberg Expires August 9, 2004 [Page 18] Internet-Draft Presence Authorization February 2004 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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