SIMPLE J. Rosenberg
Internet-Draft dynamicsoft
Expires: August 9, 2004 February 9, 2004
An Extensible Markup Language (XML) Representation for Expressing
Policy Capabilities
draft-rosenberg-simple-common-policy-caps-00
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
An important component of presence and location services is policy.
Policy systems allow the presentity or location target to grant
access to specific pieces of information to specific watchers or
requestors. These policy systems can be extremely simple, allowing a
user to accept or block requests based solely on the identity of the
requestor, to extremely complex, allowing for time based rules that
grant or deny specific pieces of information. Policy systems often
support vendor proprietary features. To allow for interoperability
between clients which set such policies, and servers which execute
them, it is necessary for clients to be able to determine the
capabilities of the server to which it is connected. This
specification defines an Extensible Markup Language (XML) based
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format for expressing such capabilities.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of Operation . . . . . . . . . . . . . . . . . . . . 3
4. Structure of Policy Capabilities . . . . . . . . . . . . . . . 4
5. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Example Document . . . . . . . . . . . . . . . . . . . . . . . 5
7. Usage with XCAP . . . . . . . . . . . . . . . . . . . . . . . 6
7.1 Application Unique ID . . . . . . . . . . . . . . . . . . . . 6
7.2 Structure of Supported Permissions . . . . . . . . . . . . . . 6
7.3 Naming Conventions . . . . . . . . . . . . . . . . . . . . . . 6
7.4 Authorization Policies . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9.1 XCAP Application Usage ID . . . . . . . . . . . . . . . . . . 7
9.2 URN Sub-Namespace Registrations . . . . . . . . . . . . . . . 8
9.3 XML Schema Registration . . . . . . . . . . . . . . . . . . . 8
Normative References . . . . . . . . . . . . . . . . . . . . . 8
Informative References . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . 10
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1. 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.
2. Introduction
An important component of presence [7] and location services [9] is
policy. Policy systems allow the presentity or location target
(referred to generically as the Presentity Target (PT)) to grant
access to specific pieces of information to specific watchers or
requestors (referred to as a WR). These policy systems can be
extremely simple, allowing a PT to accept or block requests based
solely on the identity of the WR, to extremely complex, allowing for
time based rules that grant or deny specific pieces of information.
[8] specifies a generic format for representing these policies, using
the Extensible Markup Language (XML). These policies consist of
conditions, actions, and transformations. That specification defines
very few actual conditions, actions or transformations. Rather, it
leaves such definitions to actual policy systems, such as [10] for
location services, and [11] for presence services.
In addition to the conditions, actions and transformations specificed
in the documents referenced above, policy systems often support
vendor proprietary features. It is also anticipated that future
specifications will be continually developed that add new types of
policies. This presents an interoperability challenge. Clients may
support policies that are not supported by the servers they are
using. This could lead to protocol failures or poor user experiences.
To address this problem, it is necessary for a capability declaration
system to be put in place. This specification defines a general
purpose format for representing policy capabilities within the
framework established in [8].
3. Overview of Operation
This specification defines an XML-based document format that allows a
server to represent its capabilities. When a client, acting as an
agent of a PT, starts up, it obtains this document from its policy
server. This specification does not prescribe a singular means of
transporting such a document between the server and the client. It is
anticipated that different systems may use different techniques.
However, for systems that make use of the XML Configuration Access
Protocol (XCAP) [4], Section 7 defines an application usage that
allows for the transfer of the document using XCAP.
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Once the document has been obtained by the client, it can determine
which actions, conditions and transformations are understood by the
server. This set is matched against those supported by the client.
Those actions, conditions and transformations supported by the
client, but not by the server, can be "greyed out" from a user
interface, for example.
It is anticipated that the capabilities of the server can change over
time. As a result, it is RECOMMENDED that clients obtain a fresh copy
of the capabilities document each time they start.
4. Structure of Policy Capabilities
A supported permission documentis an XML [5] document that MUST be
well-formed and SHOULD be valid. Supported permission documents MUST
be based on XML 1.0 and MUST be encoded using UTF-8. This
specification makes use of XML namespaces for identifying supported
permission documents and document fragments. The namespace URI for
elements defined for this purpose is a URN [2], using the namespace
identifier 'ietf' defined by [3] and extended by [6]. This URN is:
urn:ietf:params:xml:ns:supported-permissions
A supported permission document is structured much like a policy
document [8]. The root element is "supported-permissions". This
element has three children - "conditions", "actions", and
"transformations". Each of these contain a list of the supported
conditions, actions, and transformations, respectively. Generally
speaking, each specific condition, action or transformation element
(referred to as a capability element) is empty, unless it requires
additional content to further refine the capability.
This specification defines four capability elements - "identity",
"validity", "sphere" and "confirmation", matching the four
permissions defined in [8]. Other specifications that define
additional permissions SHOULD also define matching capability
elements.
A server constructing a document to represent its capabilities MUST
include all of those supported, even if those capabilities represent
mandatory-to-implement features. However, the server MAY indicate
differing sets of capabilities to different users. As such, the set
of capabilities combines both the ability and the willingness to
support those permissions.
5. XML Schema
<xs:schema
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targetNamespace="urn:ietf:params:xml:ns:supported-permissions"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:cp="urn:ietf:params:xml:ns:supported-permissions"
elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:element name="supported-permissions">
<xs:complexType>
<xs:sequence>
<xs:element name="conditions" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element ref="cp:condition" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="actions" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element ref="cp:action" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="transformations" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element ref="cp:transformation" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="condition" abstract="true"/>
<xs:element name="action" abstract="true"/>
<xs:element name="transformation" abstract="true"/>
<xs:element name="validity" substitutionGroup="cp:condition"/>
<xs:element name="sphere" substitutionGroup="cp:condition"/>
<xs:element name="identity" substitutionGroup="cp:condition"/>
<xs:element name="confirmation" substitutionGroup="cp:action"/>
</xs:schema>
6. Example Document
The following document indicates that the identity, validity, sphere
and confirmation attributes are supported. It also indicates that a
vendor-specific condition, called "temp", is supported, in addition
to two vendor-specific transformations - "max-security" and
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"min-security".
<?xml version="1.0" encoding="UTF-8"?>
<supported-permissions
xmlns="urn:ietf:params:xml:ns:supported-permissions"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:supported-permissions"
xmlns:vpp="http://www.vendor.com/extension1">
<conditions>
<identity/>
<validity/>
<sphere/>
<vpp:temp/>
</conditions>
<actions>
<confirmation/>
</actions>
<transformations>
<vpp:min-security/>
<vpp:max-security/>
</transformations>
</supported-permissions>
7. Usage with XCAP
The following section defines the details necessary for clients to
read supported permissions documents from a server using XCAP.
7.1 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 "supported-permissions" AUID within the
IETF tree, via the IANA registration in Section 9.
7.2 Structure of Supported Permissions
The structure of the document is defined in Section 4, and the schema
is defined in Section 5.
7.3 Naming Conventions
When a client starts, it can fetch the permissions understood by the
server in one of two places. If the server capabilities differ on a
user by user basis, the supported permissions for user foo can be
found in http://[xcap root services uri]/supported-permissions/users/
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foo/sp.xml. A client SHOULD check this file first. If this document
doesn't exist, the client should next check for the system wide
permissions by checking http://[xcap root services uri]/
supported-permissions/global/sp.xml.
7.4 Authorization Policies
By default, a user cannot modify the supported permissions document -
they can only read it. Write access is granted only to
administrators.
8. Security Considerations
Supported permission documents reveal capability information about a
server. This information can potentially be used by an enterprise to
determine the features found in competitive products. However, such
information could just as easily be obtained through other means, for
example, by signing up as a legitimate user of the competitive
service. Because supported permission documents can vary by user to
user, they can also reveal information about the grade of service
offered to a particular user. However, this information does not
appear particularly sensitive. As a result, encryption of these
documents is not terribly important.
If an attacker can modify the contents of a supported permission
document as it passes from client to server, the attacker can remove
capability elements, therefore reducing the level of service received
by the client. This can therefore form a type of denial-of-service
attack. As a result, systems which transfer these documents SHOULD
provide for message integrity.
9. IANA Considerations
There are several IANA considerations associated with this
specification.
9.1 XCAP Application Usage ID
This section registers an XCAP Application Usage ID (AUID) according
to the IANA procedures defined in [4].
Name of the AUID: supported-permissions
Description: Supported permissions are documents that describe the
types of permissions which are supported by a policy server. For
example, these permissions specify the information that watchers
[7] of presence are allowed to see.
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9.2 URN Sub-Namespace Registrations
This section registers a new XML namespace, as per the guidelines in
[6]
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:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Supported Permissions Namespace</title>
</head>
<body>
<h1>Namespace for Supported Permissions</h1>
<h2>urn:ietf:params:xml:ns:supported-permissions</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
9.3 XML Schema Registration
This section registers an XML schema as per the procedures in [6].
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.
Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Moats, R., "URN Syntax", RFC 2141, May 1997.
[3] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.
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[4] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)", draft-ietf-simple-xcap-01
(work in progress), October 2003.
[5] 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.
[6] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January
2004.
Informative References
[7] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[8] 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.
[9] Cuellar, J., Morris, J. and D. Mulligan, "Geopriv
requirements", draft-ietf-geopriv-reqs-04 (work in progress),
October 2003.
[10] Schulzrinne, H., Morris, J., Tschofenig, H., Cuellar, J. and J.
Polk, "Geopriv Authorization Rules",
draft-ietf-geopriv-rules-00 (work in progress), February 2004.
[11] Rosenberg, J., "Presence Authorization Rules",
draft-rosenberg-simple-rules-00 (work in progress), February
2004.
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
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