SIMPLE J. Rosenberg
Internet-Draft dynamicsoft
Expires: October 29, 2004 April 30, 2004
Presence Authorization Rules
draft-ietf-simple-presence-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 Subscription Handling . . . . . . . . . . . . . . . . . . 6
3.3 Transformations . . . . . . . . . . . . . . . . . . . . . 6
3.3.1 Inclusion Set . . . . . . . . . . . . . . . . . . . . . . 7
3.3.2 Provide Contact URI . . . . . . . . . . . . . . . . . . . 8
3.3.3 Provide Activity . . . . . . . . . . . . . . . . . . . . . 8
3.3.4 Provide Tuples . . . . . . . . . . . . . . . . . . . . . . 8
3.3.5 Provide Class . . . . . . . . . . . . . . . . . . . . . . 8
3.3.6 Provide Contact Type . . . . . . . . . . . . . . . . . . . 8
3.3.7 Idle Detail . . . . . . . . . . . . . . . . . . . . . . . 9
3.3.8 Provide Idle . . . . . . . . . . . . . . . . . . . . . . . 9
3.3.9 Provide PlaceType . . . . . . . . . . . . . . . . . . . . 9
3.3.10 Provide Privacy . . . . . . . . . . . . . . . . . . . . . 9
3.3.11 Provide Relationship . . . . . . . . . . . . . . . . . . . 10
3.3.12 Provide Sphere . . . . . . . . . . . . . . . . . . . . . . 10
3.3.13 Provide Unknown Status . . . . . . . . . . . . . . . . . . 10
4. Example Document . . . . . . . . . . . . . . . . . . . . . 12
5. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Schema Extensibility . . . . . . . . . . . . . . . . . . . 15
7. XCAP Usage . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1 Application Unique ID . . . . . . . . . . . . . . . . . . 16
7.2 Structure of Permission Statements . . . . . . . . . . . . 16
7.3 Additional Constraints . . . . . . . . . . . . . . . . . . 16
7.4 Naming Conventions . . . . . . . . . . . . . . . . . . . . 16
7.5 Authorization Policies . . . . . . . . . . . . . . . . . . 16
7.6 XML Schema . . . . . . . . . . . . . . . . . . . . . . . . 16
8. Security Considerations . . . . . . . . . . . . . . . . . 17
9. IANA Considerations . . . . . . . . . . . . . . . . . . . 18
9.1 XCAP Application Usage ID . . . . . . . . . . . . . . . . 18
9.2 URN Sub-Namespace Registration . . . . . . . . . . . . . . 18
9.3 XML Schema Registrations . . . . . . . . . . . . . . . . . 19
Normative References . . . . . . . . . . . . . . . . . . . 20
Informative References . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . 22
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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 [16]. 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 service 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 [16] [[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 [17], 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 any other authentication mechanism in SIP which might be
identified in other specifications, a similar pattern would be
followed.
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
3.2.1 Subscription Handling
The "sub-handling" element defines the action that the server is to
take in the processing of this subscription. It is an enumerated
integer type. The defined values are:
block: This action tells the server to reject the subscription. It
has the value of zero, and it represents the default value. No
value of the sub-handling element can ever be lower than this.
Strictly speaking, it is not necessary to every include an
explicit block action, since the default in the absence of any
action will be block. However, it is included for completeness.
confirm: This action tells the server to place the subscription in
the "pending" state, and await input from the presentity to
determine how to proceed. It has a value of one.
polite-block: 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 has a value of two.
allow: This implies that the subscription is accepted, and accurate
information, within the constraints of the transformations
specified by the rule, is supplied. This action has a value of
three.
NOTE WELL: Placing a value of block for this element does not
guarantee that a subscription is denied! If any matching rule has
any other value for this element, the subscription will receive
treatment based on the maximum of those other values. This is
based on the combining rules defined in [10].
3.3 Transformations
Each transformation defined here defines the visibility a watcher is
granted to a particular component of the presence document. Many of
these transformations are set types, as defined in [10]. In
particular, they are a specific kind of set which is defined here,
called an inclusion set.
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3.3.1 Inclusion Set
An inclusion set is used to identify a set of tuples in which a
particular presence attribute will appear. Each element in the set is
itself a presence attribute and value. If a particular presence
attribute and value exists in the set, it means that any tuple in the
document that has that particular presence attribute with that
particular value will belong to the inclusion set.
As an example, consider the following inclusion set:
o placetype=home
o class=friend
If the transformation for the RPID sphere element was an inclusion
set, and its value was the set above, it would mean that the RPID
sphere element would be included in any tuple that had a placetype
equal to home or a class equal to friend.
When represented in XML, an inclusion set is a XML data type. The
content of any element of this type is either the all-tuples element,
or a tuples-whose element. The all-tuples element is a short-hand
notation for any set that would result in the selection of every
tuple in the presence document. The tuples-whose element contains a
sequence of an RPID element and its value. Each RPID element/value is
an entry in the set. When an RPID element/value is present in the
set, it means that presence tuples that are described with that RPID
element with that value are selected. Some RPID elements include
"from" and "until" qualifiers; these are ignored for the purposes of
selection.
Because the inclusion set is a set type, composition rules follow the
union operation. This means that if one permission grants access to
the sphere element in tuples whose placetype is home, and another
permission grants access to the sphere element in tuples whose class
is friend, the result is that the sphere element will be provided in
any tuple that has a placetype of home or a class of friend.
The default value for any element of this type is empty, meaning that
the presence attribute would not be included in any tuples.
The inclusion set allows allows for extensibility by allowing other
members of the set which identify a tuple in ways besides the value
of a presence attribute within that tuple.
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3.3.2 Provide Contact URI
The "provide-contact-uri" permission indicates whether or not the
Contact URI for tuples is presented to the watcher. This element is
of the inclusion-set type, which means it is a set whose members
indicate characteristics that identify which tuples the contact URI
should be included in.
OPEN ISSUE: There is no way to define that a contact-uri applies
to all tuples without a class label. If we want that, we need to
add another selection operation to the inclusion set type, which
selects tuples in which a particular presence attribute is, or is
not, present.
3.3.3 Provide Activity
This permission controls access to the "activity" element defined in
[11]. The name of the element is "provide-activity", and it is of the
inclusion set type.
3.3.4 Provide Tuples
This permission controls access to tuples. It indicates which tuples
should be present in the document sent to a watcher. It is of the
inclusion-set type. The name of the element is "provide-tuples".
When a tuple is included, this means that its basic status and note
elements are included. Presence of the contact URI depends on the
provide-contact-uri permission, as does the presence of any other
presence attributes.
OPEN ISSUE: Because the default for the inclusion-set type is the
empty set, no tuples will be included in the presence document by
default, unless they are specifically included. We may want to
define a different type that has, as default, some agreed-upon
definition of baseline tuples.
3.3.5 Provide Class
This permission controls access to the "class" element within the
PIDF document. The name of the element is "provide-class", and it is
of the inclusion-set data type.
3.3.6 Provide Contact Type
This permission, "provide-contact-type" controls access to the
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"contact-type" element within the PIDF document. It is of the
inclusion-set data type.
3.3.7 Idle Detail
This permission, "idle-detail" defines the level of detail present in
the "idle" element within the PIDF document, wherever it appears. A
separate permission, provide-idle, determines where it will appear.
idle-detail is an enumerated integer type. Its values "no-time", with
a value of zero, that indicates that the "idle" element is to be
passed on to watchers, but without the specific duration for which
the user has been idle, and "full", with a value of one, that
indicates that the "idle" element is to be passed onto watchers, and
should include a specific duration if available.
The default value for this element is zero, meaning that no durations
are provided by default.
3.3.8 Provide Idle
This permission, "provide-idle", controls access to the RPID "idle"
element in the presence document. It is of inclusion-set type.
Because the "provide-idle" and "idle-detail" transformations are
separate and orthogonal, it is not possible to define transformations
which give a certain level of detail in some tuples, and a different
level in other tuples.
OPEN ISSUE: Is this constraint OK? It wasnt clear how to fix this
with the defined data types.
3.3.9 Provide PlaceType
This permission, "provide-placetype" controls access to the
"placetype" element within the PIDF document. It is of the
inclusion-set type.
OPEN ISSUE: Do we want any finer grained permissions than just
whether to include, or not include, placetype in the presence
document?
3.3.10 Provide Privacy
This permission, "provide-privacy" controls access to the "privacy"
element within the PIDF document. It is of the inclusion-set type.
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3.3.11 Provide Relationship
This permission, "provide-relationship" controls access to the
"relationship" element within the PIDF document. It is of the
inclusion-set type.
3.3.12 Provide Sphere
This permission, "provide-sphere" controls access to the "sphere"
element within the PIDF document. It is of the inclusion-set type.
3.3.13 Provide Unknown Status
It is important that systems be allowed to include proprietary or new
presence information, and that users be able to set permissions for
that status information, without requiring an upgrade of the presence
server and authorization system. For this reason, the
"provide-unknown-status" permission is defined. This permission
indicates that the unknown presence status with the given name
(supplied as mandatory attribute of the "provide-presence-status"
element) can be placed in the indicated tuples.
The "provide-unknown-status" element is of the
"unknown-inclusion-set" type. This type is identical to
"inclusion-set", except elements of this type have to include the
mandatory name attribute, identifying the presence status element to
which they apply. The value of the name attribute MUST be a qualified
element name (meaning that the namespace prefix MUST be included),
which will be matched to all unknown child elements of the PIDF
"status" element with the same qualified name. In this context,
"unknown" means that the presence server is not aware of any schemas
that define authorization policies for that element. By definition,
this will exclude the "provide-unknown-status" rule from being
applied to any of the presence status extensions defined by RPID.
Another consequence of this definition is that the interpretation of
the "provide-unknown-status" element can change should the presence
server be upgraded with a new schema that defines authorization rules
for elements included in a "provide-unknown-status". The
"provide-unknown-status" permissions for those elements will then be
ignored, resulting in a removal of those elements from presence
documents sent to watchers. The system remains privacy safe, but
behavior might not be as expected. Developers of systems which allow
clients to set policies are advised to check the capabilities of the
server, as defined in [15], before uploading a new authorization
document, to make sure that the behavior will be as expected.
The content of the "provide-unknown-status" element indicates the
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tuples in which that unknown element will be included. These tuples
are selected exactly as defined for elements of the type
"inclusion-set" as discussed in Section 3.3.1.
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4. Example Document
The following presence authorization document specifies permissions
for the user "user@example.com". The permissions indicate that this
user should receive all tuples, and within those tuples, the activity
element should only be included in tuples whose class is friend.
See RFCXXXX.
END Rosenberg Expires October 29, 2004 [Page 18] Internet-Draft Presence Authorization April 2004 9.3 XML Schema Registrations This section registers an XML schema per the procedures in [12]. 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. Rosenberg Expires October 29, 2004 [Page 19] Internet-Draft Presence Authorization April 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., "Common Policy", draft-ietf-geopriv-common-policy-00 (work in progress), February 2004. [11] Schulzrinne, H., "RPID -- Rich Presence Information Data Format", draft-ietf-simple-rpid-00 (work in progress), July 2003. [12] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. Rosenberg Expires October 29, 2004 [Page 20] Internet-Draft Presence Authorization April 2004 Informative References [13] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. [14] Day, M., Aggarwal, S., Mohr, G. and J. Vincent, "Instant Messaging / Presence Protocol Requirements", RFC 2779, February 2000. [15] Rosenberg, J., "An Extensible Markup Language (XML) Representation for Expressing Presence Policy Capabilities", draft-rosenberg-simple-pres-policy-caps-00 (work in progress), February 2004. [16] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work in progress), January 2003. [17] 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 October 29, 2004 [Page 21] Internet-Draft Presence Authorization April 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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