draft-ietf-kitten-sasl-oauth-09.txt   draft-ietf-kitten-sasl-oauth-10.txt 
KITTEN W. Mills KITTEN W. Mills
Internet-Draft Yahoo! Inc. Internet-Draft Yahoo! Inc.
Intended status: Standards Track T. Showalter Intended status: Standards Track T. Showalter
Expires: June 20, 2013 Expires: August 28, 2013
H. Tschofenig H. Tschofenig
Nokia Siemens Networks Nokia Siemens Networks
December 17, 2012 February 24, 2013
A set of SASL and GSS-API Mechanisms for OAuth A set of SASL and GSS-API Mechanisms for OAuth
draft-ietf-kitten-sasl-oauth-09 draft-ietf-kitten-sasl-oauth-10.txt
Abstract Abstract
OAuth enables a third-party application to obtain limited access to a OAuth enables a third-party application to obtain limited access to a
protected resource, either on behalf of a resource owner by protected resource, either on behalf of a resource owner by
orchestrating an approval interaction, or by allowing the third-party orchestrating an approval interaction, or by allowing the third-party
application to obtain access on its own behalf. application to obtain access on its own behalf.
This document defines how an application client uses credentials This document defines how an application client uses credentials
obtained via OAuth over the Simple Authentication and Security Layer obtained via OAuth over the Simple Authentication and Security Layer
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." 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 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. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. OAuth SASL Mechanism Specifications . . . . . . . . . . . . . 8 3. OAuth SASL Mechanism Specifications . . . . . . . . . . . . . 8
3.1. Initial Client Response . . . . . . . . . . . . . . . . . 9 3.1. Initial Client Response . . . . . . . . . . . . . . . . . 9
3.1.1. Reserved Key/Values . . . . . . . . . . . . . . . . . 10 3.1.1. Reserved Key/Values . . . . . . . . . . . . . . . . . 10
3.1.2. Use of the gs2-header . . . . . . . . . . . . . . . . 10 3.1.2. Use of the gs2-header . . . . . . . . . . . . . . . . 10
3.2. Server's Response . . . . . . . . . . . . . . . . . . . . 10 3.2. Server's Response . . . . . . . . . . . . . . . . . . . . 10
3.2.1. OAuth Identifiers in the SASL Context . . . . . . . . 11 3.2.1. OAuth Identifiers in the SASL Context . . . . . . . . 11
3.2.2. Server Response to Failed Authentication . . . . . . . 11 3.2.2. Server Response to Failed Authentication . . . . . . . 11
3.2.3. Completing an Error Message Sequence . . . . . . . . . 12 3.2.3. Completing an Error Message Sequence . . . . . . . . . 12
3.3. OAuth Access Token Types using Digital Signatures and 3.3. OAuth Access Token Types using Keyed Message Digests . . . 12
Keyed Message Digests . . . . . . . . . . . . . . . . . . 12
3.4. Channel Binding . . . . . . . . . . . . . . . . . . . . . 13 3.4. Channel Binding . . . . . . . . . . . . . . . . . . . . . 13
4. GSS-API OAuth Mechanism Specification . . . . . . . . . . . . 14 4. GSS-API OAuth Mechanism Specification . . . . . . . . . . . . 14
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Successful Bearer Token Exchange . . . . . . . . . . . . . 16 5.1. Successful Bearer Token Exchange . . . . . . . . . . . . . 16
5.2. OAuth 1.0a Authorization with Channel Binding . . . . . . 17 5.2. OAuth 1.0a Authorization with Channel Binding . . . . . . 17
5.3. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 18 5.3. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 18
5.4. Failed Channel Binding . . . . . . . . . . . . . . . . . . 19 5.4. Failed Channel Binding . . . . . . . . . . . . . . . . . . 19
5.5. SMTP Example of a Failed Negotiation . . . . . . . . . . . 19 5.5. SMTP Example of a Failed Negotiation . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7. Internationalization Considerations . . . . . . . . . . . . . 22 7. Internationalization Considerations . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
8.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 23 8.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 23
8.2. GSS-API Registration . . . . . . . . . . . . . . . . . . . 24 8.2. GSS-API Registration . . . . . . . . . . . . . . . . . . . 24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.1. Normative References . . . . . . . . . . . . . . . . . . . 25 9.1. Normative References . . . . . . . . . . . . . . . . . . . 25
9.2. Informative References . . . . . . . . . . . . . . . . . . 26 9.2. Informative References . . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowlegements . . . . . . . . . . . . . . . . . . . 28 Appendix A. Acknowlegements . . . . . . . . . . . . . . . . . . . 28
Appendix B. Document History . . . . . . . . . . . . . . . . . . 29 Appendix B. Document History . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction 1. Introduction
OAuth [RFC6749] enables a third-party application to obtain limited OAuth 1.0a [RFC5849] and OAuth 2.0 [RFC6749] are protocol frameworks
access to a protected resource, either on behalf of a resource owner that enable a third-party application to obtain limited access to a
by orchestrating an approval interaction, or by allowing the third- protected resource, either on behalf of a resource owner by
party application to obtain access on its own behalf. The core OAuth orchestrating an approval interaction, or by allowing the third-party
2.0 specification [RFC6749] does not define the interaction between application to obtain access on its own behalf.
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 The core OAuth 2.0 specification [RFC6749] does not define the
OAuth 2.0 [RFC6749]. 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].
+--------+ +---------------+ The main use cases for OAuth 2.0 and OAuth 1.0a have so far focused
| |--(A)- Authorization Request ->| Resource | on an HTTP-based environment only. This document integrates OAuth
| | | Owner | 1.0a and OAuth 2.0 into non-HTTP-based applications using the
| |<-(B)-- Authorization Grant ---| | 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
| |--(C)-- Authorization Grant -->| Authorization | Message Access Protocol (IMAP) [RFC3501] and SMTP [RFC5321], which is
| Client | | Server | what this memo uses in the examples.
| |<-(D)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(E)----- Access Token ------>| Resource |
| | | Server |
| |<-(F)--- Protected Resource ---| |
+--------+ +---------------+
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- | |--(A)-- Authorization Request --->| Resource | |
based protocols, such as the Internet Message Access Protocol (IMAP) | | | Owner | |Plain
[RFC3501] and SMTP [RFC5321], which is what this memo uses in the | |<-(B)------ Access Grant ---------| | |OAuth
examples. | | +---------------+ |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 The Simple Authentication and Security Layer (SASL) is a framework
for providing authentication and data security services in for providing authentication and data security services in
connection-oriented protocols via replaceable mechanisms. It connection-oriented protocols via replaceable mechanisms. It
provides a structured interface between protocols and mechanisms. provides a structured interface between protocols and mechanisms.
The resulting framework allows new protocols to reuse existing The resulting framework allows new protocols to reuse existing
mechanisms and allows old protocols to make use of new mechanisms. mechanisms and allows old protocols to make use of new mechanisms.
The framework also provides a protocol for securing subsequent The framework also provides a protocol for securing subsequent
protocol exchanges within a data security layer. protocol exchanges within a data security layer.
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(D) The authorization server authenticates the client and (D) The authorization server authenticates the client and
validates the authorization grant, and if valid issues an access validates the authorization grant, and if valid issues an access
token. token.
(E) The client requests the protected resource from the resource (E) The client requests the protected resource from the resource
server and authenticates by presenting the access token. server and authenticates by presenting the access token.
(F) The resource server validates the access token, and if valid, (F) The resource server validates the access token, and if valid,
indicates a successful authentication. indicates a successful authentication.
Steps (E) and (F) are not defined in [RFC6749] and are the main Again, steps (E) and (F) are not defined in [RFC6749] (but are
functionality specified within this document. Consequently, the described in [RFC6750] instead) and are the main functionality
message exchange shown in Figure 2 is the result of this specified within this document. Consequently, the message exchange
specification. The client will generally need to determine the shown in Figure 1 is the result of this specification. The client
authentication endpoints (and perhaps the service endpoints) before will generally need to determine the authentication endpoints (and
the OAuth 2.0 protocol exchange messages in steps (A)-(D) are perhaps the service endpoints) before the OAuth 2.0 protocol exchange
executed. The discovery of the resource owner and authorization messages in steps (A)-(D) are executed. The discovery of the
server endpoints is outside the scope of this specification. The resource owner and authorization server endpoints is outside the
client must discover those endpoints using a discovery mechanisms scope of this specification. The client must discover those
such as Webfinger using host-meta [I-D.ietf-appsawg-webfinger]. In endpoints using a discovery mechanisms, such as Webfinger using host-
band discovery is not tenable if clients support the OAuth 2.0 meta [I-D.ietf-appsawg-webfinger]. In band discovery is not tenable
password grant. Once credentials are obtained the client proceeds to if clients support the OAuth 2.0 password grant. Once credentials
steps (E) and (F) defined in this specification. 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 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 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
The reader is assumed to be familiar with the terms used in the OAuth The reader is assumed to be familiar with the terms used in the OAuth
2.0 specification [RFC6749]. 2.0 specification [RFC6749].
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Note that the IMAP SASL specification requires base64 encoding, see Note that the IMAP SASL specification requires base64 encoding, see
Section 4 of [RFC4648], not this memo. Section 4 of [RFC4648], not this memo.
3. OAuth SASL Mechanism Specifications 3. OAuth SASL Mechanism Specifications
SASL is used as an authentication framework in a variety of SASL is used as an authentication framework in a variety of
application layer protocols. This document defines the following application layer protocols. This document defines the following
SASL mechanisms for usage with OAuth: SASL mechanisms for usage with OAuth:
OAUTHBEARER: Authorization using OAuth 2.0 bearer tokens as OAUTHBEARER: OAuth 2.0 bearer tokens, as described in [RFC6750].
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 OAUTH10A: OAuth 1.0a MAC tokens (using the HMAC-SHA1 keyed
HMAC-SHA1 keyed message digest) as described in Section 3.4.2 message digest), as described in Section 3.4.2 of [RFC5849].
of [RFC5849].
OAUTH10A-PLUS: Adds channel binding [RFC5056] capability to OAUTH10A-PLUS: Adds channel binding [RFC5056] capability to
OAUTH10A for protection against man-in-the-middle attacks. 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 New extensions may be defined to add additional OAuth Access Token
Types. Such a new SASL OAuth mechanism can be added by simply Types. Such a new SASL OAuth mechanism can be added by simply
registering the new name(s) and citing this specification for the registering the new name(s) and citing this specification for the
further definition. New channel binding enabled "-PLUS" mechanisms further definition. New channel binding enabled "-PLUS" mechanisms
defined in this way MUST include message integrity protection. A defined in this way MUST include message integrity protection. A
newly defined mechanism would also need to register a new GS2 OID. newly defined mechanism would also need to register a new GS2 OID.
These mechanisms are client initiated and lock-step, the server These mechanisms are client initiated and lock-step, the server
always replying to a client message. In the case where the client always replying to a client message. In the case where the client
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port: Contains the port number represented as a decimal positive port: Contains the port number represented as a decimal positive
integer string without leading zeros to which the client integer string without leading zeros to which the client
connected. connected.
qs: The HTTP query string. In non-channel binding mechanisms qs: The HTTP query string. In non-channel binding mechanisms
this is reserved, the client SHOUD NOT send it, and has the this is reserved, the client SHOUD NOT send it, and has the
default value of "". In "-PLUS" variants this carries a single default value of "". In "-PLUS" variants this carries a single
key value pair "cbdata" for the channel binding data payload key value pair "cbdata" for the channel binding data payload
formatted as an HTTP query string. formatted as an HTTP query string.
For OAuth Access Token Types that use digital signatures or keyed For OAuth token types that use keyed message digests the client MUST
message digests the client MUST send host and port number key/values, send host and port number key/values, and the server MUST fail an
and the server MUST fail an authorization request requiring authorization request requiring keyed message digests that do not
signatures or keyed message digests that do not have host and port have host and port values. In OAuth 1.0a for example, the so-called
values. For authorization schemes that require a URI scheme as part "signature base string calculation" includes the reconstructed HTTP
of the data being signed "http" is always used. In OAuth 1.0a for URL.
example, the so-called signature base string calculation includes the
reconstructed HTTP URL.
3.1.1. Reserved Key/Values 3.1.1. Reserved Key/Values
In these mechanisms values for path, query string and post body are In these mechanisms values for path, query string and post body are
assigned default values. OAuth authorization schemes MAY define assigned default values. OAuth authorization schemes MAY define
usage of these in the SASL context and extend this specification. usage of these in the SASL context and extend this specification.
For OAuth Access Token Types that use request signatures the default For OAuth Access Token Types that use request keyed message digest
values MUST be used unless explicit values are provided in the client the default values MUST be used unless explicit values are provided
response. The following key values are reserved for future use: in the client response. The following key values are reserved for
future use:
mthd (RESERVED): HTTP method for use in signatures, the default mthd (RESERVED): HTTP method, the default value is "POST".
value is "POST".
path (RESERVED): HTTP path data, the default value is "/". path (RESERVED): HTTP path data, the default value is "/".
post (RESERVED): HTTP post data, the default value is "". post (RESERVED): HTTP post data, the default value is "".
3.1.2. Use of the gs2-header 3.1.2. Use of the gs2-header
The OAuth scheme related mechanisms are also GSS-API mechanisms, see The OAuth scheme related mechanisms are also GSS-API mechanisms, see
Section 4 for further detail. The gs2-header is used as follows: Section 4 for further detail. The gs2-header is used as follows:
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In the non "-PLUS" mechanisms the "gs2-cb-flag" MUST be set to "n" In the non "-PLUS" mechanisms the "gs2-cb-flag" MUST be set to "n"
because channel-binding [RFC5056] data is not expected. In the because channel-binding [RFC5056] data is not expected. In the
OAUTH10A-PLUS mechanism (or other -PLUS variants based on this OAUTH10A-PLUS mechanism (or other -PLUS variants based on this
specification) the "gs2-cb-flag" MUST be set appropriately by the specification) the "gs2-cb-flag" MUST be set appropriately by the
client. client.
3.2. Server's Response 3.2. Server's Response
The server validates the response per the specification for the OAuth The server validates the response per the specification for the OAuth
Access Token Types used. If the OAuth Access Token Type utilizes a Access Token Types used. If the OAuth Access Token Type utilizes a
digital signature or a keyed message digest of the request parameters keyed message digest of the request parameters then the client must
then the client must provide a client response that satisfies the provide a client response that satisfies the data requirements for
data requirements for the scheme in use. the scheme in use.
In a "-PLUS" mechanism the server examines the channel binding data, In a "-PLUS" mechanism the server examines the channel binding data,
extracts the channel binding unique prefix, and extracts the raw extracts the channel binding unique prefix, and extracts the raw
channel biding data based on the channel binding type used. It then channel biding data based on the channel binding type used. It then
computes it's own copy of the channel binding payload and compares 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. that to the payload sent by the client in the cbdata key/value.
Those two must be equal for channel binding to succeed. Those two must be equal for channel binding to succeed.
The server responds to a successfully verified client message by The server responds to a successfully verified client message by
completing the SASL negotiation. The authenticated identity reported completing the SASL negotiation. The authenticated identity reported
by the SASL mechanism is the identity securely established for the by the SASL mechanism is the identity securely established for the
client with the OAuth credential. The application, not the SASL client with the OAuth credential. The application, not the SASL
mechanism, based on local access policy determines whether the mechanism, based on local access policy determines whether the
identity reported by the mechanism is allowed access to the requested identity reported by the mechanism is allowed access to the requested
resource. Note that the semantics of the authz-id is specified by resource. Note that the semantics of the authz-id is specified by
the SASL framework [RFC4422]. the SASL framework [RFC4422].
3.2.1. OAuth Identifiers in the SASL Context 3.2.1. OAuth Identifiers in the SASL Context
OAuth access tokens may carry the authenticated identifier of the In the OAuth framework the client may be authenticated by the
resource owner and client authentication provides the authenticated authorization server and the resource owner is authenticated to the
identity of the client issuing the request to the resource server. 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 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 GSS_C_NT_USER_NAME or a comparable newly defined GSS-API name type or
name attribute [RFC6680]. name attribute [RFC6680].
3.2.2. Server Response to Failed Authentication 3.2.2. Server Response to Failed Authentication
For a failed authentication the server returns a JSON [RFC4627] For a failed authentication the server returns a JSON [RFC4627]
formatted error result, and fails the authentication. The error formatted error result, and fails the authentication. The error
result consists of the following values: result consists of the following values:
status (REQUIRED): The authorization error code. Valid error status (REQUIRED): The authorization error code. Valid error
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3.2.3. Completing an Error Message Sequence 3.2.3. Completing an Error Message Sequence
Section 3.6 of [RFC4422] explicitly prohibits additional information Section 3.6 of [RFC4422] explicitly prohibits additional information
in an unsuccessful authentication outcome. Therefore, the error in an unsuccessful authentication outcome. Therefore, the error
message is sent in a normal message. The client MUST then send an message is sent in a normal message. The client MUST then send an
additional client response consisting of a single %x01 (control A) additional client response consisting of a single %x01 (control A)
character to the server in order to allow the server to finish the character to the server in order to allow the server to finish the
exchange. exchange.
3.3. OAuth Access Token Types using Digital Signatures and Keyed 3.3. OAuth Access Token Types using Keyed Message Digests
Message Digests
OAuth Access Token Types may use digital signatures or keyed message OAuth Access Token Types may use keyed message digests and the client
digests. The client and the resource server need to perform a and the resource server may need to perform a cryptographic
cryptographic computation for integrity protection and data origin computation for integrity protection and data origin authentication.
authentication.
OAuth is designed for access to resources identified by URIs. SASL OAuth is designed for access to resources identified by URIs. SASL
is designed for user authentication, and has no facility for more is designed for user authentication, and has no facility for more
fine-grained access control. In this specification we require or fine-grained access control. In this specification we require or
define default values for the data elements from an HTTP request define default values for the data elements from an HTTP request
which allow the signature base string to be constructed properly. which allow the signature base string to be constructed properly.
The default HTTP path is "/" and the default post body is empty. The default HTTP path is "/" and the default post body is empty.
These atoms are defined as extension points so that no changes are These atoms are defined as extension points so that no changes are
needed if there is a revision of SASL which supports more specific needed if there is a revision of SASL which supports more specific
resource authorization, e.g., IMAP access to a specific folder or FTP resource authorization, e.g., IMAP access to a specific folder or FTP
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A1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39sjv7 A1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39sjv7
3.4. Channel Binding 3.4. Channel Binding
The channel binding data is carried in the "qs" (query string) key The channel binding data is carried in the "qs" (query string) key
value pair formatted as a standard HTTP query parameter with the name value pair formatted as a standard HTTP query parameter with the name
"cbdata". Channel binding requires that the channel binding data be "cbdata". Channel binding requires that the channel binding data be
integrity protected end-to-end in order to protect against man-in- integrity protected end-to-end in order to protect against man-in-
the-middle attacks. All SASL OAuth mechanisms with a "-PLUS" postfix the-middle attacks. All SASL OAuth mechanisms with a "-PLUS" postfix
MUST provide integrity protection. It should be noted that while the 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 material at the application layer and is not suitable for use with
channel bindings. channel bindings.
The channel binding data is computed by the client based on it's The channel binding data is computed by the client based on it's
choice of preferred channel binding type. As specified in [RFC5056], choice of preferred channel binding type. As specified in [RFC5056],
the channel binding information MUST start with the channel binding the channel binding information MUST start with the channel binding
unique prefix, followed by a colon (ASCII 0x3A), followed by a base64 unique prefix, followed by a colon (ASCII 0x3A), followed by a base64
encoded channel binding payload. The channel binding payload is the encoded channel binding payload. The channel binding payload is the
raw data from the channel binding type. For example, if the client raw data from the channel binding type. For example, if the client
is using tls-unique for channel binding then the raw channel binding is using tls-unique for channel binding then the raw channel binding
skipping to change at page 14, line 19 skipping to change at page 14, line 19
A SASL OAuth mechanism is also a GSS-API mechanism and the messages 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 described in Section 3 are the same with the following changes to the
GS2 related elements: GS2 related elements:
1. the GS2 header on the client's first message is excluded when 1. the GS2 header on the client's first message is excluded when
used as a GSS-API mechanism. used as a GSS-API mechanism.
2. the initial context token header is prefixed to the client's 2. the initial context token header is prefixed to the client's
first authentication message (context token), as described in 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: The GSS-API mechanism OIDs are:
o OAUTHBEARER: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]] 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]] o OAUTH10A: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]
OAuth mechanims security contexts always have the mutual_state flag o OAUTH10A-PLUS: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]
(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 The setting of the security context flags depends on the selected
successfully comparing the TLS server identity with the negotiated mechanism:
target name. Since the TLS channel is managed by the application
outside of the GSS-API mechanism, the mechanism itself is unable to o OAUTHBEARER: The mutual_state flag (GSS_C_MUTUAL_FLAG) MUST be set
confirm the name while the application is able to perform this to FALSE since the TLS protocol execution happens outside the
comparison for the mechanism. For this reason, applications MUST SASL/GSS-API method. Server-side authentication is accomplished
match the TLS server identity with the target name using the via the mandatory use of TLS at the application layer utilizing
appropriate application profile, as discussed in [RFC6125]. For SASL. Without TLS usage at the application layer protecting the
example, when SASL OAuth is run over IMAP then the IMAP profile of by OAuth Bearer Token this SASL method is insecure.
RFC 6125 is used.
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 OAuth mechanisms do not support per-message tokens or
GSS_Pseudo_random. GSS_Pseudo_random.
OAuth supports a standard generic name syntax for acceptors, such as 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 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. 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 The query, display, and exported name syntaxes for OAuth principal
names are all the same. There is no OAuth-specific name syntax; names are all the same. There is no OAuth-specific name syntax;
applications SHOULD use generic GSS-API name types, such as applications SHOULD use generic GSS-API name types, such as
GSS_C_NT_USER_NAME and GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743], GSS_C_NT_USER_NAME and GSS_C_NT_HOSTBASED_SERVICE (see Section 4 of
Section 4). The exported name token does, of course, conform to [RFC2743]). The exported name token does, of course, conform to
[RFC2743], Section 3.2, but the "NAME" part of the token should be 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 treated as a potential input string to the OAuth name normalization
rules. rules.
5. Examples 5. Examples
These examples illustrate exchanges between an IMAP and SMTP clients These examples illustrate exchanges between an IMAP and SMTP clients
and servers. and servers.
Note to implementers: The SASL OAuth method names are case Note to implementers: The SASL OAuth method names are case
insensitive. One example uses "Bearer" but that could as easily be insensitive. One example uses "Bearer" but that could as easily be
"bearer", "BEARER", or "BeArEr". "bearer", "BEARER", or "BeArEr".
5.1. Successful Bearer Token Exchange 5.1. Successful Bearer Token Exchange
This example shows a successful OAuth 2.0 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 S: * OK IMAP4rev1 Server Ready
C: t0 CAPABILITY C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR
S: t0 OK Completed S: t0 OK Completed
C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX
J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV
GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE= GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE=
S: t1 OK SASL authentication succeeded S: t1 OK SASL authentication succeeded
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S: 535 5.7.1 http://support.example.com/mail/oauth S: 535 5.7.1 http://support.example.com/mail/oauth
[connection continues...] [connection continues...]
The server returned an error message in the 334 SASL message, the The server returned an error message in the 334 SASL message, the
client responds with the required dummy response, and the server client responds with the required dummy response, and the server
finalizes the negotiation. finalizes the negotiation.
6. Security Considerations 6. Security Considerations
OAuth 1.0a and OAuth 2 allows for a variety of deployment scenarios, OAuth 1.0a and OAuth 2 allows for a variety of deployment scenarios,
and the security properties of these profiles vary. Application and the security properties of these profiles vary. As shown in
developers therefore need to understand the needs of their Figure 1 this specification is aimed to be integrated into a larger
applications before selecting a specific SASL OAuth mechanism. 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 This document specifies three SASL and GSS-API Mechanisms for OAuth
on the Access Token Type used. and each comes with different security properties.
It is possible that SASL will be authenticating a connection and the OAUTHBEARER: This mechanism borrows from OAuth 2.0 bearer tokens
life of that connection may outlast the life of the access token used [RFC6750]. It relies on the application using TLS to protect the
to establish it. This is a common problem in application protocols OAuth 2.0 Bearer Token exchange; without TLS usage at the
where connections are long-lived, and not a problem with this application layer this method is completely insecure.
mechanism per se. Servers MAY unilaterally disconnect clients in
accordance with the application protocol.
The OAuth access token (and related keying material) is not OAUTH10A: This mechanism re-uses OAuth 1.0a MAC tokens (using the
equivalent to the user's long term password. As such, care has to be HMAC-SHA1 keyed message digest), as described in Section 3.4.2 of
taken when these OAuth credentials are used for actions like changing [RFC5849]. To compute the keyed message digest in the same way
passwords (as it is possible with some protocols, e.g., XMPP). The was in RFC 5839 this specification conveys additional parameters
server SHOULD ensure that actions taken in the authenticated channel between the client and the server. This SASL/GSS-API mechanism
are appropriate to the strength of the presented credential. 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 OAUTH10A-PLUS: This mechanism adds the channel binding [RFC5056]
token provides security benefits, as described in capability to OAUTH10A for protection against man-in-the-middle
[I-D.ietf-oauth-v2-threatmodel], and OAuth 2.0 introduces refresh attacks. OAUTH10A-PLUS mandates the usage of Transport Layer
tokens to obtain new access token on the fly. Additionally, a Security (TLS) at the application layer.
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.
7. Internationalization Considerations 7. Internationalization Considerations
The identifer asserted by the OAuth authorization server about the The identifer asserted by the OAuth authorization server about the
resource owner inside the access token may be displayed to a human. 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 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 may assert the resource owner's email address to the IMAP
server for usage in an email-based application. The identifier may server for usage in an email-based application. The identifier may
therefore contain internationalized characters and an application therefore contain internationalized characters and an application
needs to ensure that the mapping between the identifier provided by needs to ensure that the mapping between the identifier provided by
skipping to change at page 26, line 36 skipping to change at page 26, line 36
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", [RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework",
RFC 6749, October 2012. RFC 6749, October 2012.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization [RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750, October 2012. Framework: Bearer Token Usage", RFC 6750, October 2012.
9.2. Informative References 9.2. Informative References
[I-D.ietf-appsawg-webfinger] [I-D.ietf-appsawg-webfinger]
Jones, P., Salgueiro, G., and J. Smarr, "WebFinger", Jones, P., Salgueiro, G., and J. Smarr, "WebFinger",
draft-ietf-appsawg-webfinger-07 (work in progress), draft-ietf-appsawg-webfinger-10 (work in progress),
December 2012. February 2013.
[I-D.ietf-oauth-json-web-token] [I-D.ietf-oauth-json-web-token]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", draft-ietf-oauth-json-web-token-05 (work in (JWT)", draft-ietf-oauth-json-web-token-06 (work in
progress), November 2012. progress), December 2012.
[I-D.ietf-oauth-v2-http-mac] [I-D.ietf-oauth-v2-http-mac]
Richer, J., Mills, W., and H. Tschofenig, "OAuth 2.0 Richer, J., Mills, W., and H. Tschofenig, "OAuth 2.0
Message Authentication Code (MAC) Tokens", Message Authentication Code (MAC) Tokens",
draft-ietf-oauth-v2-http-mac-02 (work in progress), draft-ietf-oauth-v2-http-mac-02 (work in progress),
November 2012. 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 [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003. 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 Appendix A. Acknowlegements
The authors would like to thank the members of the Kitten working The authors would like to thank the members of the Kitten working
group, and in addition and specifically: Simon Josefson, Torsten 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, This document was produced under the chairmanship of Alexey Melnikov,
Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman. The area directors Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman. The supervising area
included Stephen Farrell. directors was Stephen Farrell.
Appendix B. Document History Appendix B. Document History
[[ to be removed by RFC editor before publication as an RFC ]] [[ 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 -09
o Incorporated review by Alexey and Hannes. o Incorporated review by Alexey and Hannes.
o Clarified the three OAuth SASL mechanisms. o Clarified the three OAuth SASL mechanisms.
o Updated references o Updated references
o Extended acknowledgements o Extended acknowledgements
 End of changes. 47 change blocks. 
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