Lemonade N. Cook Internet-Draft Cloudmark Intended status: Standards Track December 8, 2008 Expires: June 11, 2009 Internet Message Access Protocol (IMAP) - URL Access Identifier Extension draft-ncook-urlauth-accessid-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 June 11, 2009. Abstract The existing IMAP URL specification (RFC5092) lists several identifiers and identifier prefixes, that can be used to restrict access to URLAUTH-generated URLs. However, these identifiers do not provide facilities for new services such as streaming. This document proposes a set of new identifiers as well as an IANA mechanism to register new identifiers for future applications. Cook Expires June 11, 2009 [Page 1] Internet-Draft IMAP URL - Access Identifier Extension December 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in this Document . . . . . . . . . . . . . . . 3 3. Additional Authorized Access Identifiers . . . . . . . . . . . 3 3.1. Existing Access Identifiers . . . . . . . . . . . . . . . . 3 3.2. Requirement for Additional Access Identifiers . . . . . . . 4 3.3. Additional Access Identifier Specification . . . . . . . . 4 3.4. Defining an access identifier for Streaming . . . . . . . . 5 4. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6.1. Access Identifier Registration Template . . . . . . . . . . 6 6.2. Stream Application Registration . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . . . 9 Cook Expires June 11, 2009 [Page 2] Internet-Draft IMAP URL - Access Identifier Extension December 2008 1. Introduction The IMAP URL specification [RFC5092] provides a way to carry authorization information in IMAP URLs. Several authorization identifiers are specified in the document, which allow URLAUTH-authorized URLs to be used only by anonymous users, authenticated users, or message submission entities. However there is no mechanism defined to create new identifiers, and overloading the existing mechanisms has security as well as administrative implications. This document describes a new identifier "stream", to be used by message streaming entities (as described in [STREAMING]), and defines an IANA registration template, which can be used to register new identifiers for future applications. 2. Conventions Used in this Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. In examples, "C:" and "S:" indicate lines sent by the client and server respectively. If a single "C:" or "S:" label applies to multiple lines, then some of the line breaks between those lines are for editorial clarity only and may not be part of the actual protocol exchange. 3. Additional Authorized Access Identifiers 3.1. Existing Access Identifiers The IMAP URL specification, IMAPURL [RFC5092], specifies the following authorized identifiers: o "authuser" - Indicating that use of this URL is limited to authenticated IMAP sessions that are logged in as any non- anonymous user o "anonymous" - Indicating that use of this URL is not restricted by session authorization identity Additionally the following identifier prefixes are defined: o "submit+" - Followed by a userid, indicating that only a userid authorized as a message submission entity on behalf of the Cook Expires June 11, 2009 [Page 3] Internet-Draft IMAP URL - Access Identifier Extension December 2008 specified userid is permitted to use this URL o "user+" - Followed by a userid, indicating that use of this URL is limited to IMAP sessions that are logged in as the specified userid 3.2. Requirement for Additional Access Identifiers The existing identifiers are suitable for user-based authorization, but only the "submit+" identifier prefix is suitable for entities acting on behalf of a users, which is required for new services such as streaming [STREAMING]. The "submit+" identifier prefix is not suitable for use as a general mechanism to grant access to entities acting on behalf of users, for reasons that include: o Security - The IMAP server maintains a list of submission server entities that are entitled to retrieve IMAP URLs specifying the "submit+" identifier prefix. If this list is extended to include the set of all external entities that could act on behalf of users, then the attack surface would be increased. o Administration - When URLAUTH-style IMAP URLs are presented to an IMAP server by entities acting on behalf of users, the server administrator has no way of determining the intended use of that URL from the server logs. o Resourcing - Without a mechanism to distinguish between the application for which an IMAP URL is to be used, the IMAP server has no way to prioritize resources for particular applications. For example, the server could prioritize "submit+" URL fetch requests over other access identifiers. 3.3. Additional Access Identifier Specification The previous section established that additional access identifiers are required to support applications, such as streaming [STREAMING], that require entities to retrieve URLAUTH URLs on behalf of users. This section describes the scope and meaning of any additional identifiers that are created. Additional identifiers MUST take one of two forms (Section 4 gives the formal ABNF syntax): o identifier - The name of the application e.g. "stream" Cook Expires June 11, 2009 [Page 4] Internet-Draft IMAP URL - Access Identifier Extension December 2008 o identifier prefix - The name of the application e.g. "stream+" followed by a user id. For example "stream+ncook". In both cases, the semantics are the same as those for "submit+", i.e. the identifier or identifier prefix (which MUST be followed by a userid), indicates that only a userid authorized as an application entity for the specified application is permitted to use this URL. The IMAP server SHALL NOT validate any specified userid but MUST validate that the IMAP session has an authorization identity that is authorized as an application entity for the specified application. The application entity itself MAY choose to perform validation on any specified userid before attempting to retrieve the URL. The authorization granted by any identifiers used as described above is self-describing, and so requires the IMAP server to provide an extensible mechanism for associating userids with new applications. For example, imgine a new application "foo" is created, which requires application entities to retrieve URLs on behalf of users. In this case, the IMAP server would need to provide a way to register a new application "foo", and to associate the set of userids to be used by those entities with the application "foo". Any attempt to retrieve URLs containing the identifier "foo" would be be checked for authorization against the list of userids associated with the application "foo". Section 6 provides the template required to register new identifiers or prefixes with IANA. 3.4. Defining an access identifier for Streaming One application that makes use of URLAUTH-authorized URLs is that of streaming multimedia files received as internet messaging attachments. This application is described in [STREAMING]. See Section 6.2 for the IANA registration template for the "stream" identifier. 4. Formal Syntax The following syntax specification uses the Augmented Backus-Naur Form (ABNF) notation as specified in [RFC5234]. Except as noted otherwise, all alphabetic characters are case- insensitive. The use of upper or lower case characters to define token strings is for editorial clarity only. Implementations MUST accept these strings in a case-insensitive fashion. Cook Expires June 11, 2009 [Page 5] Internet-Draft IMAP URL - Access Identifier Extension December 2008 The ABNF specified below updates and replaces the formal syntax of identifier as defined in IMAP URL [RFC5092]. application = *ALPHA access = ("submit+" enc-user) / ("user+" enc-user) / "authuser" / "anonymous" / application / (application "+" enc-user) 5. Acknowledgements This document was inspired by discussions in the Lemonade Working Group. 6. IANA Considerations Access identifiers and prefixes MUST be specified in a standards track or IESG approved experimental RFC. 6.1. Access Identifier Registration Template To: iana@iana.org Subject: IMAP URL Access Identifier Registration Type: [Either "access identifier" or "access prefix"] Application: [Name of the application, e.g. "stream"] Description: [A description of the application and its use of IMAP URLs] RFC Number: [Number of the RFC that the application was defined in ] Contact: [email and/or physical address to contact for additional information] Cook Expires June 11, 2009 [Page 6] Internet-Draft IMAP URL - Access Identifier Extension December 2008 6.2. Stream Application Registration To: iana@iana.org Subject: IMAP URL Access Identifier Registration Type: access identifier Application: stream Description: Used by SIP Media Servers to retrieve attachments for streaming to email clients RFC Number: This RFC Contact: Neil Cook mailto:neil.cook@noware.co.uk 7. Security Considerations The extension to identifiers specified in this document provides a mechanism for extending the semantics of the "submit+" prefix to arbitrary applications. The use of such additional identifiers and prefixes is primarily for security purposes, i.e. to prevent the overloading of "submit+" as a generic mechanism to allow entities to retrieve IMAP URLs on behalf of userids. However, the security implications are identical to that discussed in Section 10.1 of IMAPURL [RFC5092]. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5092] Melnikov, A. and C. Newman, "IMAP URL Scheme", RFC 5092, November 2007. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. 8.2. Informative References [STREAMING] Cook, N., "Streaming Internet Messaging Attachments", Cook Expires June 11, 2009 [Page 7] Internet-Draft IMAP URL - Access Identifier Extension December 2008 draft-ietf-lemonade-streaming-08.txt (Work in Progress) , Dec 2008. Author's Address Neil L Cook Cloudmark Email: neil.cook@noware.co.uk Cook Expires June 11, 2009 [Page 8] Internet-Draft IMAP URL - Access Identifier Extension December 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Cook Expires June 11, 2009 [Page 9]