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 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 9, 2004. Copyright Notice 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 Rosenberg Expires August 9, 2004 [Page 1] Internet-Draft Common Policy Capabilities February 2004 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 Rosenberg Expires August 9, 2004 [Page 2] Internet-Draft Common Policy Capabilities February 2004 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. Rosenberg Expires August 9, 2004 [Page 3] Internet-Draft Common Policy Capabilities February 2004 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 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 Rosenberg Expires August 9, 2004 [Page 5] Internet-Draft Common Policy Capabilities February 2004 "min-security". 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/ Rosenberg Expires August 9, 2004 [Page 6] Internet-Draft Common Policy Capabilities February 2004 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. Rosenberg Expires August 9, 2004 [Page 7] Internet-Draft Common Policy Capabilities February 2004 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 Supported Permissions Namespace

Namespace for Supported Permissions

urn:ietf:params:xml:ns:supported-permissions

See RFCXXXX.

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. Rosenberg Expires August 9, 2004 [Page 8] Internet-Draft Common Policy Capabilities February 2004 [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 Rosenberg Expires August 9, 2004 [Page 9] Internet-Draft Common Policy Capabilities 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. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION Rosenberg Expires August 9, 2004 [Page 10] Internet-Draft Common Policy Capabilities February 2004 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Rosenberg Expires August 9, 2004 [Page 11]