--- 1/draft-ietf-kitten-sasl-oauth-09.txt 2013-02-24 21:31:30.671790599 +0100 +++ 2/draft-ietf-kitten-sasl-oauth-10.txt 2013-02-24 21:31:30.711790829 +0100 @@ -1,21 +1,21 @@ KITTEN W. Mills Internet-Draft Yahoo! Inc. Intended status: Standards Track T. Showalter -Expires: June 20, 2013 +Expires: August 28, 2013 H. Tschofenig Nokia Siemens Networks - December 17, 2012 + February 24, 2013 A set of SASL and GSS-API Mechanisms for OAuth - draft-ietf-kitten-sasl-oauth-09 + draft-ietf-kitten-sasl-oauth-10.txt Abstract OAuth enables a third-party application to obtain limited access to a protected resource, either on behalf of a resource owner by orchestrating an approval interaction, or by allowing the third-party application to obtain access on its own behalf. This document defines how an application client uses credentials obtained via OAuth over the Simple Authentication and Security Layer @@ -39,25 +39,25 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." - This Internet-Draft will expire on June 20, 2013. + This Internet-Draft will expire on August 28, 2013. Copyright Notice - Copyright (c) 2012 IETF Trust and the persons identified as the + Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as @@ -68,86 +68,98 @@ 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. OAuth SASL Mechanism Specifications . . . . . . . . . . . . . 8 3.1. Initial Client Response . . . . . . . . . . . . . . . . . 9 3.1.1. Reserved Key/Values . . . . . . . . . . . . . . . . . 10 3.1.2. Use of the gs2-header . . . . . . . . . . . . . . . . 10 3.2. Server's Response . . . . . . . . . . . . . . . . . . . . 10 3.2.1. OAuth Identifiers in the SASL Context . . . . . . . . 11 3.2.2. Server Response to Failed Authentication . . . . . . . 11 3.2.3. Completing an Error Message Sequence . . . . . . . . . 12 - 3.3. OAuth Access Token Types using Digital Signatures and - Keyed Message Digests . . . . . . . . . . . . . . . . . . 12 + 3.3. OAuth Access Token Types using Keyed Message Digests . . . 12 3.4. Channel Binding . . . . . . . . . . . . . . . . . . . . . 13 4. GSS-API OAuth Mechanism Specification . . . . . . . . . . . . 14 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.1. Successful Bearer Token Exchange . . . . . . . . . . . . . 16 5.2. OAuth 1.0a Authorization with Channel Binding . . . . . . 17 5.3. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 18 5.4. Failed Channel Binding . . . . . . . . . . . . . . . . . . 19 5.5. SMTP Example of a Failed Negotiation . . . . . . . . . . . 19 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 7. Internationalization Considerations . . . . . . . . . . . . . 22 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 8.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 23 8.2. GSS-API Registration . . . . . . . . . . . . . . . . . . . 24 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 9.1. Normative References . . . . . . . . . . . . . . . . . . . 25 9.2. Informative References . . . . . . . . . . . . . . . . . . 26 Appendix A. Acknowlegements . . . . . . . . . . . . . . . . . . . 28 Appendix B. Document History . . . . . . . . . . . . . . . . . . 29 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32 1. Introduction - OAuth [RFC6749] enables a third-party application to obtain limited - access to a protected resource, either on behalf of a resource owner - by orchestrating an approval interaction, or by allowing the third- - party application to obtain access on its own behalf. The core OAuth - 2.0 specification [RFC6749] does not define the interaction between - the client and the resource server with the access to a protected - resource using an Access Token. This functionality is described in - separate specifications, for example bearer tokens [RFC6750], OAuth - 2.0 MAC tokens [I-D.ietf-oauth-v2-http-mac]. OAuth 1.0a [RFC5849], - the predecessor of OAuth 2.0, has a similar design. The main use - cases for OAuth 2.0 and OAuth 1.0 have so far focused on an HTTP- - based environment only. + OAuth 1.0a [RFC5849] and OAuth 2.0 [RFC6749] are protocol frameworks + that enable a third-party application to obtain limited access to a + protected resource, either on behalf of a resource owner by + orchestrating an approval interaction, or by allowing the third-party + application to obtain access on its own behalf. - Figure 1 shows the abstract message flow as shown in Figure 1 of - OAuth 2.0 [RFC6749]. + The core OAuth 2.0 specification [RFC6749] does not define the + interaction between the OAuth client and the resource server for the + access to a protected resource using an Access Token. Instead, this + functionality is described in separate specifications, such as the + bearer token specification [RFC6750]. OAuth 1.0a included the + communication between the OAuth client and the resource server in + [RFC5849]. - +--------+ +---------------+ - | |--(A)- Authorization Request ->| Resource | - | | | Owner | - | |<-(B)-- Authorization Grant ---| | - | | +---------------+ - | | - | | +---------------+ - | |--(C)-- Authorization Grant -->| Authorization | - | Client | | Server | - | |<-(D)----- Access Token -------| | - | | +---------------+ - | | - | | +---------------+ - | |--(E)----- Access Token ------>| Resource | - | | | Server | - | |<-(F)--- Protected Resource ---| | - +--------+ +---------------+ + The main use cases for OAuth 2.0 and OAuth 1.0a have so far focused + on an HTTP-based environment only. This document integrates OAuth + 1.0a and OAuth 2.0 into non-HTTP-based applications using the + integration into SASL and the GSS-API. Hence, this document takes + advantage of the OAuth protocol and its deployment base to provide a + way to use SASL [RFC4422] and the GSS-API [RFC2743] to gain access to + resources when using non-HTTP-based protocols, such as the Internet + Message Access Protocol (IMAP) [RFC3501] and SMTP [RFC5321], which is + what this memo uses in the examples. - Figure 1: Abstract OAuth 2.0 Protocol Flow + To illustrate the impact of integrating this specification into an + OAuth-enabled application environment Figure 1 shows the abstract + message flow of OAuth 2.0 [RFC6749]. As indicated in the figure, + this document impacts the exchange of messages (E) and (F) since SASL + or the GSS-API is used for interaction between the client and the + resource server instead of HTTP. - This document takes advantage of the OAuth protocol and its - deployment base to provide a way to use SASL [RFC4422] as well as the - GSS-API [RFC2743] to gain access to resources when using non-HTTP- - based protocols, such as the Internet Message Access Protocol (IMAP) - [RFC3501] and SMTP [RFC5321], which is what this memo uses in the - examples. + ----+ + +--------+ +---------------+ | + | |--(A)-- Authorization Request --->| Resource | | + | | | Owner | |Plain + | |<-(B)------ Access Grant ---------| | |OAuth + | | +---------------+ |2.0 + | | | + | | Client Credentials & +---------------+ | + | |--(C)------ Access Grant -------->| Authorization | | + | Client | | Server | | + | |<-(D)------ Access Token ---------| | | + | | (w/ Optional Refresh Token) +---------------+ | + | | ----+ + | | ----+ + | | +---------------+ | + | | | | |OAuth + | |--(E)------ Access Token -------->| Resource | |over + | | | Server | |SASL/ + | |<-(F)---- Protected Resource -----| | |GSS- + | | | | |API + +--------+ +---------------+ | + ----+ + + Figure 1: OAuth 2.0 Protocol Flow The Simple Authentication and Security Layer (SASL) is a framework for providing authentication and data security services in connection-oriented protocols via replaceable mechanisms. It provides a structured interface between protocols and mechanisms. The resulting framework allows new protocols to reuse existing mechanisms and allows old protocols to make use of new mechanisms. The framework also provides a protocol for securing subsequent protocol exchanges within a data security layer. @@ -186,58 +198,38 @@ (D) The authorization server authenticates the client and validates the authorization grant, and if valid issues an access token. (E) The client requests the protected resource from the resource server and authenticates by presenting the access token. (F) The resource server validates the access token, and if valid, indicates a successful authentication. - Steps (E) and (F) are not defined in [RFC6749] and are the main - functionality specified within this document. Consequently, the - message exchange shown in Figure 2 is the result of this - specification. The client will generally need to determine the - authentication endpoints (and perhaps the service endpoints) before - the OAuth 2.0 protocol exchange messages in steps (A)-(D) are - executed. The discovery of the resource owner and authorization - server endpoints is outside the scope of this specification. The - client must discover those endpoints using a discovery mechanisms - such as Webfinger using host-meta [I-D.ietf-appsawg-webfinger]. In - band discovery is not tenable if clients support the OAuth 2.0 - password grant. Once credentials are obtained the client proceeds to - steps (E) and (F) defined in this specification. - - ----+ - +--------+ +---------------+ | - | |--(A)-- Authorization Request --->| Resource | | - | | | Owner | |Plain - | |<-(B)------ Access Grant ---------| | |OAuth - | | +---------------+ |2.0 - | | | - | | Client Credentials & +---------------+ | - | |--(C)------ Access Grant -------->| Authorization | | - | Client | | Server | | - | |<-(D)------ Access Token ---------| | | - | | (w/ Optional Refresh Token) +---------------+ | - | | ----+ - | | ----+ - | | +---------------+ | - | | | | |OAuth - | |--(E)------ Access Token -------->| Resource | |over - | | | Server | |SASL/ - | |<-(F)---- Protected Resource -----| | |GSS- - | | | | |API - +--------+ +---------------+ | - ----+ + Again, steps (E) and (F) are not defined in [RFC6749] (but are + described in [RFC6750] instead) and are the main functionality + specified within this document. Consequently, the message exchange + shown in Figure 1 is the result of this specification. The client + will generally need to determine the authentication endpoints (and + perhaps the service endpoints) before the OAuth 2.0 protocol exchange + messages in steps (A)-(D) are executed. The discovery of the + resource owner and authorization server endpoints is outside the + scope of this specification. The client must discover those + endpoints using a discovery mechanisms, such as Webfinger using host- + meta [I-D.ietf-appsawg-webfinger]. In band discovery is not tenable + if clients support the OAuth 2.0 password grant. Once credentials + are obtained the client proceeds to steps (E) and (F) defined in this + specification. - Figure 2: OAuth SASL Architecture + OAuth 1.0 follows a similar model but uses a different terminology + and does not separate the resource server from the authorization + server. 2. Terminology 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 [RFC2119]. The reader is assumed to be familiar with the terms used in the OAuth 2.0 specification [RFC6749]. @@ -246,29 +238,32 @@ Note that the IMAP SASL specification requires base64 encoding, see Section 4 of [RFC4648], not this memo. 3. OAuth SASL Mechanism Specifications SASL is used as an authentication framework in a variety of application layer protocols. This document defines the following SASL mechanisms for usage with OAuth: - OAUTHBEARER: Authorization using OAuth 2.0 bearer tokens as - described in [RFC6750]. + OAUTHBEARER: OAuth 2.0 bearer tokens, as described in [RFC6750]. + RFC 6750 uses Transport Layer Security (TLS) to secure the + protocol interaction between the client and the resource + server. - OAUTH10A: Authorization using OAuth 1.0a MAC tokens (using the - HMAC-SHA1 keyed message digest) as described in Section 3.4.2 - of [RFC5849]. + OAUTH10A: OAuth 1.0a MAC tokens (using the HMAC-SHA1 keyed + message digest), as described in Section 3.4.2 of [RFC5849]. OAUTH10A-PLUS: Adds channel binding [RFC5056] capability to OAUTH10A for protection against man-in-the-middle attacks. + OAUTH10A-PLUS mandates the usage of Transport Layer Security + (TLS). New extensions may be defined to add additional OAuth Access Token Types. Such a new SASL OAuth mechanism can be added by simply registering the new name(s) and citing this specification for the further definition. New channel binding enabled "-PLUS" mechanisms defined in this way MUST include message integrity protection. A newly defined mechanism would also need to register a new GS2 OID. These mechanisms are client initiated and lock-step, the server always replying to a client message. In the case where the client @@ -321,40 +316,38 @@ port: Contains the port number represented as a decimal positive integer string without leading zeros to which the client connected. qs: The HTTP query string. In non-channel binding mechanisms this is reserved, the client SHOUD NOT send it, and has the default value of "". In "-PLUS" variants this carries a single key value pair "cbdata" for the channel binding data payload formatted as an HTTP query string. - For OAuth Access Token Types that use digital signatures or keyed - message digests the client MUST send host and port number key/values, - and the server MUST fail an authorization request requiring - signatures or keyed message digests that do not have host and port - values. For authorization schemes that require a URI scheme as part - of the data being signed "http" is always used. In OAuth 1.0a for - example, the so-called signature base string calculation includes the - reconstructed HTTP URL. + For OAuth token types that use keyed message digests the client MUST + send host and port number key/values, and the server MUST fail an + authorization request requiring keyed message digests that do not + have host and port values. In OAuth 1.0a for example, the so-called + "signature base string calculation" includes the reconstructed HTTP + URL. 3.1.1. Reserved Key/Values In these mechanisms values for path, query string and post body are assigned default values. OAuth authorization schemes MAY define usage of these in the SASL context and extend this specification. - For OAuth Access Token Types that use request signatures the default - values MUST be used unless explicit values are provided in the client - response. The following key values are reserved for future use: + For OAuth Access Token Types that use request keyed message digest + the default values MUST be used unless explicit values are provided + in the client response. The following key values are reserved for + future use: - mthd (RESERVED): HTTP method for use in signatures, the default - value is "POST". + mthd (RESERVED): HTTP method, the default value is "POST". path (RESERVED): HTTP path data, the default value is "/". post (RESERVED): HTTP post data, the default value is "". 3.1.2. Use of the gs2-header The OAuth scheme related mechanisms are also GSS-API mechanisms, see Section 4 for further detail. The gs2-header is used as follows: @@ -368,49 +361,52 @@ In the non "-PLUS" mechanisms the "gs2-cb-flag" MUST be set to "n" because channel-binding [RFC5056] data is not expected. In the OAUTH10A-PLUS mechanism (or other -PLUS variants based on this specification) the "gs2-cb-flag" MUST be set appropriately by the client. 3.2. Server's Response The server validates the response per the specification for the OAuth Access Token Types used. If the OAuth Access Token Type utilizes a - digital signature or a keyed message digest of the request parameters - then the client must provide a client response that satisfies the - data requirements for the scheme in use. + keyed message digest of the request parameters then the client must + provide a client response that satisfies the data requirements for + the scheme in use. In a "-PLUS" mechanism the server examines the channel binding data, extracts the channel binding unique prefix, and extracts the raw channel biding data based on the channel binding type used. It then computes it's own copy of the channel binding payload and compares that to the payload sent by the client in the cbdata key/value. Those two must be equal for channel binding to succeed. The server responds to a successfully verified client message by completing the SASL negotiation. The authenticated identity reported by the SASL mechanism is the identity securely established for the client with the OAuth credential. The application, not the SASL mechanism, based on local access policy determines whether the identity reported by the mechanism is allowed access to the requested resource. Note that the semantics of the authz-id is specified by the SASL framework [RFC4422]. 3.2.1. OAuth Identifiers in the SASL Context - OAuth access tokens may carry the authenticated identifier of the - resource owner and client authentication provides the authenticated - identity of the client issuing the request to the resource server. + In the OAuth framework the client may be authenticated by the + authorization server and the resource owner is authenticated to the + authorization server. OAuth access tokens may contain information + about the authentication of the resource owner and about the client + and may therefore make this information accessible to the resource + server. - If both identities are needed by an application the developer will + If both identifiers are needed by an application the developer will need to provide a way to communicate that from the SASL mechanism - back to the application such as a GSS-API [RFC2743] named type like + back to the application, such as a GSS-API [RFC2743] named type like GSS_C_NT_USER_NAME or a comparable newly defined GSS-API name type or name attribute [RFC6680]. 3.2.2. Server Response to Failed Authentication For a failed authentication the server returns a JSON [RFC4627] formatted error result, and fails the authentication. The error result consists of the following values: status (REQUIRED): The authorization error code. Valid error @@ -435,27 +431,25 @@ 3.2.3. Completing an Error Message Sequence Section 3.6 of [RFC4422] explicitly prohibits additional information in an unsuccessful authentication outcome. Therefore, the error message is sent in a normal message. The client MUST then send an additional client response consisting of a single %x01 (control A) character to the server in order to allow the server to finish the exchange. -3.3. OAuth Access Token Types using Digital Signatures and Keyed - Message Digests +3.3. OAuth Access Token Types using Keyed Message Digests - OAuth Access Token Types may use digital signatures or keyed message - digests. The client and the resource server need to perform a - cryptographic computation for integrity protection and data origin - authentication. + OAuth Access Token Types may use keyed message digests and the client + and the resource server may need to perform a cryptographic + computation for integrity protection and data origin authentication. OAuth is designed for access to resources identified by URIs. SASL is designed for user authentication, and has no facility for more fine-grained access control. In this specification we require or define default values for the data elements from an HTTP request which allow the signature base string to be constructed properly. The default HTTP path is "/" and the default post body is empty. These atoms are defined as extension points so that no changes are needed if there is a revision of SASL which supports more specific resource authorization, e.g., IMAP access to a specific folder or FTP @@ -498,21 +492,21 @@ A1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39sjv7 3.4. Channel Binding The channel binding data is carried in the "qs" (query string) key value pair formatted as a standard HTTP query parameter with the name "cbdata". Channel binding requires that the channel binding data be integrity protected end-to-end in order to protect against man-in- the-middle attacks. All SASL OAuth mechanisms with a "-PLUS" postfix MUST provide integrity protection. It should be noted that while the - Bearer Access Token Type mandates TLS it does not create keying + OAuth 2.0 Bearer Token mandates TLS it does not create keying material at the application layer and is not suitable for use with channel bindings. The channel binding data is computed by the client based on it's choice of preferred channel binding type. As specified in [RFC5056], the channel binding information MUST start with the channel binding unique prefix, followed by a colon (ASCII 0x3A), followed by a base64 encoded channel binding payload. The channel binding payload is the raw data from the channel binding type. For example, if the client is using tls-unique for channel binding then the raw channel binding @@ -526,74 +520,95 @@ A SASL OAuth mechanism is also a GSS-API mechanism and the messages described in Section 3 are the same with the following changes to the GS2 related elements: 1. the GS2 header on the client's first message is excluded when used as a GSS-API mechanism. 2. the initial context token header is prefixed to the client's first authentication message (context token), as described in - Section 3.1 of RFC 2743, + Section 3.1 of RFC 2743 [RFC2743], The GSS-API mechanism OIDs are: o OAUTHBEARER: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]] o OAUTH10A: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]] - OAuth mechanims security contexts always have the mutual_state flag - (GSS_C_MUTUAL_FLAG) set to TRUE. OAuth supports credential - delegation, therefore security contexts may have the deleg_state flag - (GSS_C_DELEG_FLAG) set to either TRUE or FALSE. + o OAUTH10A-PLUS: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]] - The mutual authentication property of this mechanism relies on - successfully comparing the TLS server identity with the negotiated - target name. Since the TLS channel is managed by the application - outside of the GSS-API mechanism, the mechanism itself is unable to - confirm the name while the application is able to perform this - comparison for the mechanism. For this reason, applications MUST - match the TLS server identity with the target name using the - appropriate application profile, as discussed in [RFC6125]. For - example, when SASL OAuth is run over IMAP then the IMAP profile of - RFC 6125 is used. + The setting of the security context flags depends on the selected + mechanism: + + o OAUTHBEARER: The mutual_state flag (GSS_C_MUTUAL_FLAG) MUST be set + to FALSE since the TLS protocol execution happens outside the + SASL/GSS-API method. Server-side authentication is accomplished + via the mandatory use of TLS at the application layer utilizing + SASL. Without TLS usage at the application layer protecting the + by OAuth Bearer Token this SASL method is insecure. + + o OAUTH10A: The mutual_state flag (GSS_C_MUTUAL_FLAG) MUST be set to + FALSE since server authentication is not provided by this SASL/ + GSS-API method. Since the TLS channel is managed by the + application outside of the GSS-API mechanism, the OAUTH10A + mechanism itself is unable to confirm the name while the + application is able to perform this comparison for the mechanism. + For this reason, applications MUST match the TLS server identity + with the target name using the appropriate application profile, as + discussed in [RFC6125]. For example, when SASL OAuth is run over + IMAP then the IMAP profile of RFC 6125 is used. + + o OAUTH10A-PLUS: The mutual_state flag (GSS_C_MUTUAL_FLAG) MUST be + set to FALSE since only the client demonstrates possession of the + session key by applying a keyed message digest function over + various fields of the request. TLS-based server-side + authentication MUST be provided by the application using SASL. + + Credential delegation is not supported by any of the SASL/GSS-API + mechanisms with this specification. Therefore, security contexts + MUST have the deleg_state flag (GSS_C_DELEG_FLAG) set to FALSE. OAuth mechanisms do not support per-message tokens or GSS_Pseudo_random. OAuth supports a standard generic name syntax for acceptors, such as - GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743], Section 4.1). These + GSS_C_NT_HOSTBASED_SERVICE (see Section 4.1 of [RFC2743]). These service names MUST be associated with the "entityID" claimed by the - RP. OAuth mechanisms support only a single name type for initiators: + RP. + + OAuth mechanisms support only a single name type for initiators: GSS_C_NT_USER_NAME. GSS_C_NT_USER_NAME is the default name type. + The query, display, and exported name syntaxes for OAuth principal names are all the same. There is no OAuth-specific name syntax; applications SHOULD use generic GSS-API name types, such as - GSS_C_NT_USER_NAME and GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743], - Section 4). The exported name token does, of course, conform to - [RFC2743], Section 3.2, but the "NAME" part of the token should be + GSS_C_NT_USER_NAME and GSS_C_NT_HOSTBASED_SERVICE (see Section 4 of + [RFC2743]). The exported name token does, of course, conform to + Section 3.2 of [RFC2743], but the "NAME" part of the token should be treated as a potential input string to the OAuth name normalization rules. 5. Examples These examples illustrate exchanges between an IMAP and SMTP clients and servers. Note to implementers: The SASL OAuth method names are case insensitive. One example uses "Bearer" but that could as easily be "bearer", "BEARER", or "BeArEr". 5.1. Successful Bearer Token Exchange This example shows a successful OAuth 2.0 bearer token exchange. - Note that line breaks are inserted for readability. + Note that line breaks are inserted for readability and the underlying + TLS establishment is not shown either. S: * OK IMAP4rev1 Server Ready C: t0 CAPABILITY S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR S: t0 OK Completed C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE= S: t1 OK SASL authentication succeeded @@ -751,49 +766,51 @@ S: 535 5.7.1 http://support.example.com/mail/oauth [connection continues...] The server returned an error message in the 334 SASL message, the client responds with the required dummy response, and the server finalizes the negotiation. 6. Security Considerations OAuth 1.0a and OAuth 2 allows for a variety of deployment scenarios, - and the security properties of these profiles vary. Application - developers therefore need to understand the needs of their - applications before selecting a specific SASL OAuth mechanism. + and the security properties of these profiles vary. As shown in + Figure 1 this specification is aimed to be integrated into a larger + OAuth deployment. Application developers therefore need to + understand the needs of their security requirements based on a threat + assessment before selecting a specific SASL OAuth mechanism. For + OAuth 2.0 a detailed security document [RFC6819] provides guidance to + select those OAuth 2.0 components that help to mitigate threats for a + given deployment. For OAuth 1.0a Section 4 of RFC 5849 [RFC5849] + provides guidance specific to OAuth 1.0. - The channel binding in this mechanism has different properties based - on the Access Token Type used. + This document specifies three SASL and GSS-API Mechanisms for OAuth + and each comes with different security properties. - It is possible that SASL will be authenticating a connection and the - life of that connection may outlast the life of the access token used - to establish it. This is a common problem in application protocols - where connections are long-lived, and not a problem with this - mechanism per se. Servers MAY unilaterally disconnect clients in - accordance with the application protocol. + OAUTHBEARER: This mechanism borrows from OAuth 2.0 bearer tokens + [RFC6750]. It relies on the application using TLS to protect the + OAuth 2.0 Bearer Token exchange; without TLS usage at the + application layer this method is completely insecure. - The OAuth access token (and related keying material) is not - equivalent to the user's long term password. As such, care has to be - taken when these OAuth credentials are used for actions like changing - passwords (as it is possible with some protocols, e.g., XMPP). The - server SHOULD ensure that actions taken in the authenticated channel - are appropriate to the strength of the presented credential. + OAUTH10A: This mechanism re-uses OAuth 1.0a MAC tokens (using the + HMAC-SHA1 keyed message digest), as described in Section 3.4.2 of + [RFC5849]. To compute the keyed message digest in the same way + was in RFC 5839 this specification conveys additional parameters + between the client and the server. This SASL/GSS-API mechanism + only supports client authentication. If server-side + authentication is desireable then it must be provided by the + application underneath the SASL/GSS-API layer. - Access tokens have a lifetime. Reducing the lifetime of an access - token provides security benefits, as described in - [I-D.ietf-oauth-v2-threatmodel], and OAuth 2.0 introduces refresh - tokens to obtain new access token on the fly. Additionally, a - previously obtained access token MAY be revoked or rendered invalid - at any time. The client MAY request a new access token for each - connection to a resource server, but it SHOULD cache and re-use - access credentials that appear to be valid. + OAUTH10A-PLUS: This mechanism adds the channel binding [RFC5056] + capability to OAUTH10A for protection against man-in-the-middle + attacks. OAUTH10A-PLUS mandates the usage of Transport Layer + Security (TLS) at the application layer. 7. Internationalization Considerations The identifer asserted by the OAuth authorization server about the resource owner inside the access token may be displayed to a human. For example, when SASL is used in the context of IMAP the resource server may assert the resource owner's email address to the IMAP server for usage in an email-based application. The identifier may therefore contain internationalized characters and an application needs to ensure that the mapping between the identifier provided by @@ -930,57 +947,61 @@ [RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 6749, October 2012. [RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization Framework: Bearer Token Usage", RFC 6750, October 2012. 9.2. Informative References [I-D.ietf-appsawg-webfinger] Jones, P., Salgueiro, G., and J. Smarr, "WebFinger", - draft-ietf-appsawg-webfinger-07 (work in progress), - December 2012. + draft-ietf-appsawg-webfinger-10 (work in progress), + February 2013. [I-D.ietf-oauth-json-web-token] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token - (JWT)", draft-ietf-oauth-json-web-token-05 (work in - progress), November 2012. + (JWT)", draft-ietf-oauth-json-web-token-06 (work in + progress), December 2012. [I-D.ietf-oauth-v2-http-mac] Richer, J., Mills, W., and H. Tschofenig, "OAuth 2.0 Message Authentication Code (MAC) Tokens", draft-ietf-oauth-v2-http-mac-02 (work in progress), November 2012. - [I-D.ietf-oauth-v2-threatmodel] - Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0 - Threat Model and Security Considerations", - draft-ietf-oauth-v2-threatmodel-08 (work in progress), - October 2012. - [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, March 2003. + [RFC6819] Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0 + Threat Model and Security Considerations", RFC 6819, + January 2013. + Appendix A. Acknowlegements The authors would like to thank the members of the Kitten working group, and in addition and specifically: Simon Josefson, Torsten - Lodderstadt, Ryan Troll, Alexey Melnikov, and Nico Williams. + Lodderstadt, Ryan Troll, Alexey Melnikov, Jeffrey Hutzelman, and Nico + Williams. This document was produced under the chairmanship of Alexey Melnikov, - Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman. The area directors - included Stephen Farrell. + Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman. The supervising area + directors was Stephen Farrell. Appendix B. Document History [[ to be removed by RFC editor before publication as an RFC ]] + -10 + + o Clarifications throughout the document in response to the feedback + from Jeffrey Hutzelman. + -09 o Incorporated review by Alexey and Hannes. o Clarified the three OAuth SASL mechanisms. o Updated references o Extended acknowledgements