| KITTEN | W. Mills |
| Internet-Draft | Yahoo! Inc. |
| Intended status: Standards Track | T. Showalter |
| Expires: June 20, 2013 | H. Tschofenig |
| Nokia Siemens Networks | |
| December 17, 2012 |
A set of SASL and GSS-API Mechanisms for OAuth
draft-ietf-kitten-sasl-oauth-09
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 (SASL) or the Generic Security Service Application Program Interface (GSS-API) to access a protected resource at a resource serve. Thereby, it enables schemes defined within the OAuth framework for non-HTTP-based application protocols.
Clients typically store the user's long-term credential. This does, however, lead to significant security vulnerabilities, for example, when such a credential leaks. A significant benefit of OAuth for usage in those clients is that the password is replaced by a token. Tokens typically provided limited access rights and can be managed and revoked separately from the user's long-term credential (password).
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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/⁠.
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This Internet-Draft will expire on June 20, 2013.
Copyright (c) 2012 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 described in the Simplified BSD License.
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.
Figure 1 shows the abstract message flow as shown in Figure 1 of OAuth 2.0 [RFC6749].
+--------+ +---------------+
| |--(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 ---| |
+--------+ +---------------+
Figure 1: Abstract OAuth 2.0 Protocol Flow
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.
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.
The Generic Security Service Application Program Interface (GSS-API) [RFC2743] provides a framework for applications to support multiple authentication mechanisms through a unified interface.
This document defines SASL mechanisms for OAuth, and it conforms to the new bridge between SASL and the GSS-API called GS2 [RFC5801]. This means that this document defines both SASL and GSS-API mechanisms. Implementers may be interested in either the SASL, the GSS-API, or even both mechanisms. To facilitate these two variants, the description has been split into two parts, one part that provides normative references for those interested in the SASL OAuth mechanism (see Section 3), and a second part for those implementers that wish to implement the GSS-API portion (see Section 4).
When OAuth is integrated into SASL and the GSS-API the high-level steps are as follows:
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
+--------+ +---------------+ |
----+
Figure 2: OAuth SASL Architecture
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].
In examples, "C:" and "S:" indicate lines sent by the client and server respectively. Line breaks have been inserted for readability.
Note that the IMAP SASL specification requires base64 encoding, see Section 4 of [RFC4648], not this memo.
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:
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 has and correctly uses a valid token the flow is:
In the case where authorization fails the server sends an error result, then client MUST then send an additional message to the server in order to allow the server to finish the exchange. Some protocols and common SASL implementations do not support both sending a SASL message and finalizing a SASL negotiation, the additional client message in the error case deals with this problem. This exchange is:
Client responses are a key/value pair sequence. The initial client response includes a gs2-header as defined in GS2 [RFC5801], which carries the authorization ID. These key/value pairs carry the equivalent values from an HTTP context in order to be able to complete an OAuth style HTTP authorization. Unknown key/value pairs MUST be ignored by the server. The ABNF [RFC5234] syntax is:
kvsep = %x01
key = 1*ALPHA
value = *(VCHAR / SP / HTAB / CR / LF )
kvpair = key "=" value kvsep
client_resp = 0*kvpair kvsep
;; gs2-header = As defined in GSS-API
initial_client_resp = gs2-header kvsep client_resp
The following key/value pairs are defined in the client response:
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.
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:
The OAuth scheme related mechanisms are also GSS-API mechanisms, see Section 4 for further detail. The gs2-header is used as follows:
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.
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.
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].
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.
If both identities 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 GSS_C_NT_USER_NAME or a comparable newly defined GSS-API name type or name attribute [RFC6680].
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:
If the resource server provides a scope then the client MUST always request scoped tokens from the token endpoint. If the resource server provides no scope to the client then the client SHOULD presume an empty scope (unscoped token) is needed.
If channel binding is in use and the channel binding fails the server responds with a status code set to 412 to indicate that the channel binding precondition failed. If the authentication scheme in use does not include signing the server SHOULD revoke the presented credential and the client SHOULD discard that credential.
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.
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 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 access limited to a specific directory.
Using the example in the OAuth 1.0a specification as a starting point, on an IMAP server running on port 143 and given the OAuth 1.0a style authorization request (with %x01 shown as ^A and line breaks added for readability) below:
n,a=user@example.com^A
host=example.com^A
user=user@example.com^A
port=143^A
auth=OAuth realm="Example",
oauth_consumer_key="9djdj82h48djs9d2",
oauth_token="kkk9d7dh3k39sjv7",
oauth_signature_method="HMAC-SHA1",
oauth_timestamp="137131201",
oauth_nonce="7d8f3e4a",
oauth_signature="Tm90IGEgcmVhbCBzaWduYXR1cmU%3D"^A^A
The signature base string would be constructed per the OAuth 1.0 specification [RFC5849] with the following things noted:
In this example the signature base string with line breaks added for readability would be:
POST&http%3A%2F%2Fexample.com:143%2F&oauth_consumer_key%3D9djdj82h4 8djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_method%3DHMAC-SH A1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39sjv7
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 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 data is the TLS finished message as specified in Section 3.1 of [RFC5929].
Note: The normative references in this section are informational for SASL implementers, but they are normative for GSS-API implementers.
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:
The GSS-API mechanism OIDs are:
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.
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.
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 service names MUST be associated with the "entityID" claimed by the 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 treated as a potential input string to the OAuth name normalization rules.
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".
This example shows a successful OAuth 2.0 bearer token exchange. Note that line breaks are inserted for readability.
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
As required by IMAP [RFC3501], the payloads are base64-encoded. The decoded initial client response (with %x01 represented as ^A and long lines wrapped for readability) is:
n,a=user@example.com^Ahost=server.example.com^Aport=143^A auth=Bearer vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg==^A^A
The same credential used in an SMTP exchange is shown below. Note that line breaks are inserted for readability, and that the SMTP protocol terminates lines with CR and LF characters (ASCII values 0x0D and 0x0A), these are not displayed explicitly in the example.
[connection begins]
S: 220 mx.example.com ESMTP 12sm2095603fks.9
C: EHLO sender.example.com
S: 250-mx.example.com at your service,[172.31.135.47]
S: 250-SIZE 35651584
S: 250-8BITMIME
S: 250-AUTH LOGIN PLAIN OAUTHBEARER
S: 250-ENHANCEDSTATUSCODES
S: 250 PIPELINING
C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX
J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV
GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE=
S: 235 Authentication successful.
[connection continues...]
This example shows channel binding in the context of an OAuth 1.0a request using a keyed message digest. Note that line breaks are inserted for readability.
S: * OK [CAPABILITY IMAP4rev1 AUTH=OAUTH10A-PLUS SASL-IR]
IMAP4rev1 Server Ready
C: t1 AUTHENTICATE OAUTH10A-PLUS cD10bHMtdW5pcXVlLGE9dXNlckBleGFtcGxlL
mNvbQFob3N0PXNlcnZlci5leGFtcGxlLmNvbQFwb3J0PTE0MwFhdXRoPU9BdXRoI
HJlYWxtPSJFeGFtcGxlIixvYXV0aF9jb25zdW1lcl9rZXk9IjlkamRqODJoNDhka
nM5ZDIiLG9hdXRoX3Rva2VuPSJra2s5ZDdkaDNrMzlzanY3IixvYXV0aF9zaWduY
XR1cmVfbWV0aG9kPSJITUFDLVNIQTEiLG9hdXRoX3RpbWVzdGFtcD0iMTM3MTMxM
jAxIixvYXV0aF9ub25jZT0iN2Q4ZjNlNGEiLG9hdXRoX3NpZ25hdHVyZT0iU1Nkd
ElHRWdiR2wwZEd4bElIUmxZU0J3YjNRdSIBcXM9Y2JkYXRhPXRscy11bmlxdWU6U
0c5M0lHSnBaeUJwY3lCaElGUk1VeUJtYVc1aGJDQnRaWE56WVdkbFB3bz0BAQ==
S: t1 OK SASL authentication succeeded
As required by IMAP [RFC3501], the payloads are base64-encoded. The decoded initial client response (with %x01 represented as ^A and lines wrapped for readability) is:
p=tls-unique,a=user@example.com^A
host=server.example.com^A
port=143^A
auth=OAuth realm="Example",
oauth_consumer_key="9djdj82h48djs9d2",
oauth_token="kkk9d7dh3k39sjv7",
oauth_signature_method="HMAC-SHA1",
oauth_timestamp="137131201",
oauth_nonce="7d8f3e4a",
oauth_signature="SSdtIGEgbGl0dGxlIHRlYSBwb3Qu"^A
qs=cbdata=tls-unique:SG93IGJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=^A^A
POST&http%3A%2F%2Fserver.example.com:143%2F&cbdata=tls-unique:SG93I GJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=%26oauth_consumer_key%3D9djd j82h48djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_method%3DHM AC-SHA1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39s jv7
This example shows a failed exchange because of the empty Authorization header, which is how a client can query for the needed scope. Note that line breaks are inserted for readability.
S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR IMAP4rev1 Server
Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTHBEARER cD10bHMtdW5pcXVlLGE9dXNlckBleGFtcG
xlLmNvbQFob3N0PXNlcnZlci5leGFtcGxlLmNvbQFwb3J0PTE0MwFhdXRoP
QFjYmRhdGE9AQE=
S: + ewoic3RhdHVzIjoiNDAxIgoic2NvcGUiOiJleGFtcGxlX3Njb3BlIgp9
C: + AQ==
S: t1 NO SASL authentication failed
The decoded initial client response is:
n,a=user@example.com,^Ahost=server.example.com^A
port=143^Aauth=^A^A
The decoded server error response is:
{
"status":"401",
"scope":"example_scope"
}
The client responds with the required dummy response.
This example shows a channel binding failure in an empty request. The channel binding information is empty. Note that line breaks are inserted for readability.
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH10A-PLUS SASL-IR IMAP4rev1 Server
Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH10A-PLUS cCxhPXVzZXJAZXhhbXBsZS5jb20BaG9z
dD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD0BY2JkYXRhPQEB
S: + ewoic3RhdHVzIjoiNDEyIiwKInNjb3BlIjoiZXhhbXBsZV9zY29wZSIKfQ==
C: + AQ==
S: t1 NO SASL authentication failed
The decoded initial client response is:
p=tls-unique,a=user@example.com,^Ahost=server.example.com^A
port=143^Aauth=^Acbdata=^A^A
The decoded server response is:
{
"status":"412",
"scope":"example_scope"
}
The client responds with the required dummy response.
This example shows an authorization failure in an SMTP exchange. Note that line breaks are inserted for readability, and that the SMTP protocol terminates lines with CR and LF characters (ASCII values 0x0D and 0x0A), these are not displayed explicitly in the example.
[connection begins]
S: 220 mx.example.com ESMTP 12sm2095603fks.9
C: EHLO sender.example.com
S: 250-mx.example.com at your service,[172.31.135.47]
S: 250-SIZE 35651584
S: 250-8BITMIME
S: 250-AUTH LOGIN PLAIN OAUTHBEARER
S: 250-ENHANCEDSTATUSCODES
S: 250 PIPELINING
C: AUTH OAUTHBEARER bixhPT1zb21ldXNlckBleGFtcGxlLmNvbQFhdXRoPUJlYXJlciB2
RjlkZnQ0cW1UYzJOdmIzUmxja0JoZEhSaGRtbHpkR0V1WTI5dENnPT0BAQ==
S: 334 eyJzdGF0dXMiOiI0MDEiLCJzY2hlbWVzIjoiYmVhcmVyIG1hYyIsInNjb3BlIjoia
HR0cHM6Ly9tYWlsLmdvb2dsZS5jb20vIn0K
C: AQ==
S: 535-5.7.1 Username and Password not accepted. Learn more at
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.
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.
The channel binding in this mechanism has different properties based on the Access Token Type used.
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.
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.
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.
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 OAuth is suitable for use with the application layer protocol SASL is incorporated into.
At the time of writing the standardization of the assertion format (in JSON format) is still ongoing, see [I-D.ietf-oauth-json-web-token].
The IANA is requested to register the following SASL profile:
The IANA is requested to register the following SASL profile:
The IANA is requested to register the following SASL profile:
IANA is further requested to assign an OID for these GSS mechanisms in the SMI numbers registry, with the prefix of iso.org.dod.internet.security.mechanisms (1.3.6.1.5.5) and to reference this specification in the registry.
| [RFC3501] | Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, March 2003. |
| [I-D.ietf-appsawg-webfinger] | Jones, P, Salgueiro, G and J Smarr, "WebFinger", Internet-Draft draft-ietf-appsawg-webfinger-00, July 2012. |
| [I-D.ietf-oauth-json-web-token] | Jones, M, Bradley, J and N Sakimura, "JSON Web Token (JWT)", Internet-Draft draft-ietf-oauth-json-web-token-00, May 2012. |
| [I-D.ietf-oauth-v2-http-mac] | Hammer-Lahav, E, "HTTP Authentication: MAC Access Authentication", Internet-Draft draft-ietf-oauth-v2-http-mac-01, February 2012. |
| [I-D.ietf-oauth-v2-threatmodel] | Lodderstedt, T, McGloin, M and P Hunt, "OAuth 2.0 Threat Model and Security Considerations", Internet-Draft draft-ietf-oauth-v2-threatmodel-08, October 2012. |
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.
This document was produced under the chairmanship of Alexey Melnikov, Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman. The area directors included Stephen Farrell.
[[ to be removed by RFC editor before publication as an RFC ]]
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