wdiff draft-ietf-kitten-sasl-oauth-00.txt draft-ietf-kitten-sasl-oauth-01.txt

KITTEN W. Mills
Internet-Draft T. Showalter Yahoo! Inc.
Intended status: Standards Track Yahoo! Inc. T. Showalter
Expires: May 17, December 1, 2012
H. Tschofenig
Nokia Siemens Networks
November 14, 2011
May 30, 2012

A SASL and GSS-API Mechanism for OAuth
draft-ietf-kitten-sasl-oauth-00.txt
draft-ietf-kitten-sasl-oauth-01

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 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, and additionally defines
authorization and token issuing endpoint discovery. 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).

Status of this Memo

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
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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 May 17, December 1, 2012.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. OAuth SASL Mechanism Specification . . . . . . . . . . . . . . 8
3.1. Channel Binding . . . . . . . . . . . . . . . . . . . . . 8
3.2. Initial Client Response . . . . . . . . . . . . . . . . . 8
3.2.1. Query String
3.1.1. Reserved Key/Values in OAUTH-PLUS . OAUTH . . . . . . . . . . . . . 9
3.3. 8
3.2. Server's Response . . . . . . . . . . . . . . . . . . . . 9
3.4.
3.2.1. Mapping to SASL Identities . . . . . . . . . . . . . . 9
3.2.2. Server response to failed authentication. . . . . . . 10
3.5. Discovery Information
3.3. Use of Signature Type Authorization . . . . . . . . . . . 10
3.4. Channel Binding . . . . . . . 10
3.6. Use of Signature Type Authorization . . . . . . . . . . . 12 . . . 11
4. GSS-API OAuth Mechanism Specification . . . . . . . . . . . . 14 12
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 13
5.1. Successful Bearer Token Exchange . . . . . . . . . . . . . 15 13
5.2. MAC Authentication with Channel Binding . . . . . . . . . 15 13
5.3. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 16 14
5.4. Failed Channel Binding . . . . . . . . . . . . . . . . . . 17 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 17
7.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 19 17
7.2. GSS-API Registration . . . . . . . . . . . . . . . . . . . 19
7.3. Link Type Registration . . . . . . . . . . . . . . . . . . 19
7.3.1. OAuth 2 Authentication Endpoint . . . . . . . . . . . 19
7.3.2. OAuth 2 Token Endpoint . . . . . . . . . . . . . . . . 20
7.3.3. OAuth 1.0a Request Initiation Endpoint . . . . . . . . 20
7.3.4. OAuth 1.0a Authorization Endpoint . . . . . . . . . . 21
7.3.5. OAuth 1.0a Token Endpoint . . . . . . . . . . . . . . 21 17
8. Appendix A -- Document History . . . . . . . . . . . . . . . . 22 18
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 19
9.1. Normative References . . . . . . . . . . . . . . . . . . . 23 19
9.2. Informative References . . . . . . . . . . . . . . . . . . 24 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25 21

1. Introduction

OAuth [I-D.ietf-oauth-v2] 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 specification [I-D.ietf-oauth-v2] 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 two separate specifications, namely
[I-D.ietf-oauth-v2-bearer], and [I-D.ietf-oauth-v2-http-mac], whereby
the focus is on an HTTP-based environment only.

Figure 1 shows the abstract message flow as shown in Figure 1 of
[I-D.ietf-oauth-v2].

+--------+ +---------------+
| |--(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], 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 a SASL mechanism for OAuth, but it conforms to
the new bridge between SASL and the GSS-API called GS2 [RFC5801].
This means that this document defines both a SASL mechanism and a
GSS-API mechanism. Implementers may be interested in either the
SASL, the GSS-API, or even both mechanisms. To faciliate 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:

(A) The client requests authorization from the resource owner.
The authorization request can be made directly to the resource
owner (as shown), or preferably indirectly via the authorization
server as an intermediary.

(B) The client receives an authorization grant which is a
credential representing the resource owner's authorization,
expressed using one of four grant types defined in this
specification or using an extension grant type. The authorization
grant type depends on the method used by the client to request
authorization and the types supported by the authorization server.

(C) The client requests an access token by authenticating with the
authorization server and presenting the authorization grant.

(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,
serves the request.

Steps (E) and (F) are not defined in [I-D.ietf-oauth-v2] and are the
main functionality specified within this document. Additionally, an
optional discovery exchange is defined. Consequently, the
message exchange shown in Figure 2 is the result of this
specification. (1)
and (2) denote The client will genrally need to determine the optional discovery exchange steps that may happen
authentication endpoints (and perhaps the service endpoints) before
the OAuth 2.0 protocol exchange messages in steps (A)-(D) are
executed. Steps (E) The discovery of the resource owner and (F) also defined in authorization
server endpoints is outside the scope of this specification.

----+
+--------+ +---------------+ |
| |--(A)-- Authorization Request --->| Resource | | The
client must discover those endpoints using a discovery mechanisms
such as Webfinger using host-meta [I-D.jones-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) +---------------+ |
| | ----+
| |
| | ----+
| | (Optional discovery) +---------------+ |
| |--(1)------- User Name --------->| | |
| Client | | | |
| |<-(2)------ Authentication -------| | |
| | endpoint information | Resource | |OAuth
| | | Server | |over
| |--(E)------ Access Token -------->| Resource | |SASL/ |over
| | | Server | |GSS- |SASL/
| |<-(F)---- Protected Resource -----| | |GSS-
| | | | |API
+--------+ +---------------+ |
----+

Figure 2: OAuth SASL Architecture

Note: The discovery procedure in OAuth is still work in progress.
Hence, the discovery components described in this document should
be considered incomplete and a tentative proposal. In general,
there is a trade off between a generic, externally available
defined discovery mechanisms (such as Webfinger using host-meta
[I-D.hammer-hostmeta], or [I-D.jones-simple-web-discovery]) and
configuration information exchanged in-band between the SASL
communication endpoints.

It is worthwhile to note that this specification is also compatible
with OAuth 1.0a [RFC5849].

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 [I-D.ietf-oauth-v2].

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
message, not this memo.

3. OAuth SASL Mechanism Specification

SASL is used as a generalized authentication method in a variety of
application layer protocols. This document defines two SASL
mechanisms for usage with OAuth: "OAUTH" and "OAUTH-PLUS". The
"OAUTH" SASL mechanism provides bearer token alike semantic enables OAuth authorizattion schemes for SASL
while SASL,
"OAUTH-PLUS" provides a semantic similar to OAuth MAC
authentication by utilizing a adds channel binding mechanism [RFC5056].

3.1. Channel Binding

If the specification [RFC5056] capability for the underlying authorization scheme requires
a additional
security layer, such as TLS [RFC5246], the server SHOULD only offer guarantees.

3.1. Initial Client Response

Client responses are a mechanism where channel binding can key/value pair sequence. These key/value
pairs carry the equivalent values form an HTTP context in order to be enabled.
able to complete an OAuth style HTTP authorization. The channel binding data is computed by the client based on it's
choice of preferred channel binding type. As specified ABNF
[RFC2234] syntax is:

kvsep = %x01
key = 1*ALPHA
value = *(VCHAR | SP | HTAB | CR | LF )
kvpair = key "=" value kvsep
client_resp = 1*kvpair kvsep

The following key/value pairs are defined 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. client response:

auth (REQUIRED): The channel binding payload is of the
raw data from the channel binding type if the raw channel binding
data is less than 500 bytes. If the raw channel binding data is 500
bytes or larger then a SHA-1 [RFC3174] hash of the raw channel
binding data is computed.

If the client is using tls-unique HTTP Authorization header for a channel binding then the raw
channel binding data equals the first TLS finished message. This is
under the 500 byte limit, so the channel binding payload sent to the
server would be the base64 encoded first TLS finished message.

In the case where the client has chosen tls-endpoint, the raw channel
binding data is the certificate of the server the client connected
to, which will frequently be 500 bytes or more. If it is then the
channel binding payload is the base64 encoded SHA-1 hash of the
server certificate.

3.2. Initial Client Response

The SASL client response is formatted as
an equivalent HTTP [RFC2616] request.
The HTTP request is limited in that the path MUST be "/". In the
OAUTH mechanism no query string is allowed. The following header
lines are defined in the client response:

User (OPTIONAL): Contains the user identifier being
authenticated, and is provided to allow correct discovery
information to be returned.

Host (REQUIRED): OAuth authroization.

host: Contains the host name to which the client connected.

Authorization (REQUIRED): An HTTP Authorization header.

The user name is provided by the client to allow the discovery
information to be customized for the user, a given server could allow
multiple authenticators and it needs to return the correct one. For
instance, a large ISP could provide mail service for several domains
who manage their own user information. For instance, users at foo-
example.com could be authenticated by an OAuth service at
https://oauth.foo-example.com/, and users at bar-example.com could be
authenticated by https://oauth.bar-example.com, but both could be
served by a hypothetical IMAP server running at a third domain,
imap.example.net.

3.2.1. Query String in OAUTH-PLUS

In the OAUTH-PLUS mechanism the channel binding information is
carried in the query string. OAUTH-PLUS defines following query
parameter(s):

cbdata (REQUIRED):

port: Contains the base64 encoded channel binding
data, properly escaped as an HTML query parameter value.

3.3. Server's Response

The server validates the response per the specification for the
authorization scheme used. If the authorization scheme used includes
signing of the request parameters the client must provide a complete
HTTP style request that satisfies the data requirements for the
scheme in use.

In the OAUTH-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 query
parameters of the tunneled HTTP request. 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 authentication scheme MUST
carry the user ID to be used as the authorization identity (identity
to act as). The server MUST use that ID as the user being
authorized, that is the user assertion we accept and not other
information such as from the URL or "User:" header.

The server responds to failed authentication by sending discovery
information in an HTTP style response with the HTTP status code set
to 401, and then failing the authentication.

If channel binding is in use and the channel binding fails the server
responds with a minimal HTTP response without discovery information
and the HTTP 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.

3.4. Mapping to SASL Identities

Some OAuth mechanisms can provide both an authorization identity and
an authentication identity. An example of this is OAuth 1.0a
[RFC5849] where the consumer key (oauth_consumer_key) identifies the
entity using the port number represented as a decimal positive
integer string without leading zeros to token which equates to the SASL authentication
identity, and is authenticated using the shared secret. The client
connected.

In authorization identity in the OAuth 1.0a case is carried in schemes that use signatures, the token
(per client MUST send
host and port number key/values, and the requirement above), which SHOULD validated independently.
The server MAY use a consumer key or other comparable identity MUST fail
authorization request requiring signatures that do not have host and
port values.

3.1.1. Reserved Key/Values in OAUTH

In the OAUTH mechanism values for path, query string and post body
are assigned default values. OAuth authorization scheme as schemes MAY define
usage of these in the SASL authentication identity. If
an appropriate authentication identity is not available the server
MUST context and extend this specification.
For OAuth schemes that use the identity asserted in the token.

3.5. Discovery Information

The server MUST send discovery information in response to a failed
authentication exchange or a request with an empty Authorization
header. If discovery information is returned it MUST include an
authentication endpoint appropriate for the user. If the "User"
header is present signatures the discovery information default values MUST
be for that user.
Discovery information is used unless explict values are provided by the server to in the client to
allow a client to discover the appropriate OAuth authentication and
token endpoints. response.
The client then uses that information to obtain the
access token needed following key values are reserved for OAuth authentication. The client SHOULD
cache and re-use future use:

path (RESERVED): HTTP path data, the user specific discovery information for service
endpoints.

Discovery information makes use of both default value is "/".

qs (RESERVED): HTTP query string, the WWW-Authenticate header
as defined in default value is "".

post (RESERVED): HTTP Authentication: Basic and Digest Access
Authentication [RFC2617] and Link headers as defined in [RFC5988]. post data, the default value is "".

3.2. Server's Response

The following elements are defined for discovery information:

WWW-Authenticate A WWW-Authenticate header server validates the response per the specification for each authentication the
authorization scheme supported by used. If the server. Authentication authorization scheme names are
case insensitive. The following [RFC2617] authentication used includes
signing of the request parameters are defined:

realm REQUIRED -- (as defined by RFC2617)

scope OPTIONAL -- A quoted string. This provides the client an
OAuth 2 scope known to be valid must provide a client
response that satisfies the data requirements for the resource.

oauth2-authenticator An [RFC5988] Link header specifying scheme in use.

In the
[I-D.ietf-oauth-v2] authentication endpoint. This link has an
OPTIONAL link-extension "scheme", if included this link applies
ONLY to OAUTH-PLUS mechanism the specified scheme.

oauth2-token An [RFC5988] Link header specifying server examines the
[I-D.ietf-oauth-v2] token endpoint. This link has an OPTIONAL
link-extension "scheme", if included this link applies ONLY to channel binding
data, extracts the
specified scheme.

oauth-initiate (Optional) An [RFC5988] Link header specifying channel binding unique prefix, and extracts the
OAuth1.0a [RFC5849] initiation endpoint. The server MUST send
this if "OAuth" is included in
raw channel biding data based on the supported list channel binding type used. It
then computes it's own copy of HTTP
authentication schemes for the server.

oauth-authorize (Optional) An [RFC5988] Link header specifying channel binding payload and
compares that to the
OAuth1.0a [RFC5849] authentication endpoint. payload sent by the client in the cbdata key/
value. Those two must be equal for channel binding to succeed.

The server MUST send
this if "OAuth" is included in responds to a successfully verified client message by
completing the supported list of HTTP SASL negotiation. The authentication schemes for scheme MUST
carry the server.

oauth-token (Optional) An [RFC5988] Link header specifying user ID to be used as the
OAuth1.0a [RFC5849] token endpoint. authorization identity (identity
to act as). The server MUST send this if
"OAuth" is included in use the supported list of HTTP authentication
schemes for ID obtained from the server. This link type has one link-extension
"grant-types" which is a space separated list credential
as the user being authorized.

3.2.1. Mapping to SASL Identities

Some OAuth mechanisms can provide both an authorization identity and
an authentication identity. An example of the this is OAuth 2.0
grant types that can be used at 1.0a
[RFC5849] where the consumer key (oauth_consumer_key) identifies the
entity using to token endpoint which equates to obtain a
token.

Usage of the URLs provided SASL authentication
identity, and is authenticated using the shared secret. The
authorization identity in the discovery information OAuth 1.0a case is defined carried in the relevant specifications. If token
(per the requirement above), which SHOULD validated independently.
The server supports multiple
authenticators the discovery information returned for unknown users
MUST be consistent with MAY use a consumer key, a value derived from it, or other
comparable identity in the discovery information for known users to
prevent user enumeration. The OAuth 2.0 specification
[I-D.ietf-oauth-v2] supports multiple types of authorization scheme as the SASL
authentication schemes
and identity. If an appropriate authentication identity
is not available the server MUST specify at least one supported use the authorization identity as
the wuthentication identity.

3.2.2. Server response to failed authentication.

For a failed authentication
scheme in the discovery information. The server MAY support multiple
schemes returns a JSON [RFC4627]
formatted error result, and MAY support schemes not listed fails the authentication. The error
result consists of the following values:

status (REQUIRED): The authorization error code. Valid error
codes are defined in the discovery
information. IANA [[need registry name]] registry
specified in the OAuth 2 core specification.

scope (OPTIONAL): The OAuth scope required to access the service.

If the resource server provides a scope the client SHOULD always
request scoped tokens from the token endpoint. The client MAY use a
scope other than the one provided by the resource server. Scopes
other than those advertised by the resource server must are be defined by
the resource owner and provided in service documentation or discovery
information (which is beyond the scope of this memo).

3.6. If not present
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.

3.3. Use of Signature Type Authorization

This mechanism supports authorization using signatures, which
requires that both client and server construct the string to be
signed. OAuth 2 is designed for authentication/authorization to
access specific URIs. SASL is designed for user authentication, and
has no facility for being more specific. In this mechanism we
require or define default values for the data elements from an HTTP style format specifically to support
request which allow the signature type
authentication, but this is extremely limited. base string to be constructed
properly. The default HTTP style
request is limited to a path of "/". This mechanism is in "/" and the SASL
model, but default post body is designed
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 specific directory.

Using the example in the MAC specification
[I-D.ietf-oauth-v2-http-mac] as a starting point, on an IMAP server
running on port 143 and given the MAC style authorization request
(with %x01 shown as ^A and long lines wrapped for readability) below:

host=server.example.com^A
port=143^A
auth=MAC token="h480djs93hd8",timestamp="137131200",nonce="dj83hs9s",
signature="YTVjyNSujYs1WsDurFnvFi4JK6o="^A^A

The normalized request string would be constructed per the MAC
specification [I-D.ietf-oauth-v2-http-mac]. In this example the
normalized request string with the new line separator character is
represented by "\n" for display purposes only would be:

h480djs93hi8\n
137131200\n
dj83hs9s\n
\n
GET\n
server.example.com\n
143\n
/\n
\n

3.4. Channel Binding

If the specification for the underlying authorization scheme requires
a security layer, such as TLS [RFC5246], the server SHOULD only offer
a mechanism where channel binding can be enabled.

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 if the raw channel binding
data is less than 500 bytes. If the raw channel binding data is 500
bytes or larger then a SHA-1 [RFC3174] hash of the raw channel
binding data is computed.

If the client is using tls-unique for a channel binding then the example in raw
channel binding data equals the MAC specification
[I-D.ietf-oauth-v2-http-mac] as a starting point, on an IMAP server
running on port 143 and given first TLS finished message. This is
under the MAC style authorization request
(with long lines wrapped for readability) below:

GET / HTTP/1.1
Host: server.example.com
User: user@example.com
Authorization: MAC token="h480djs93hd8",timestamp="137131200",
nonce="dj83hs9s",signature="YTVjyNSujYs1WsDurFnvFi4JK6o="

The normalized request string 500 byte limit, so the channel binding payload sent to the
server would be constructed per the MAC
specification [I-D.ietf-oauth-v2-http-mac]. base64 encoded first TLS finished message.

In this example the
normalized request string with case where the new line separator character client has chosen tls-endpoint, the raw channel
binding data is
represented by "\n" for display purposes only would be:

h480djs93hi8\n
137131200\n
dj83hs9s\n
\n
GET\n
server.example.com\n
143\n
/\n
\n the certificate of the server the client connected
to, which will frequently be 500 bytes or more. If it is then the
channel binding payload is the base64 encoded SHA-1 hash of the
server certificate.

4. GSS-API OAuth Mechanism Specification

Note: The normative references in this section are informational for
SASL implementers, but they are normative for GSS-API implementers.

The SASL OAuth mechanism is also a GSS-API mechanism and the messages
described in Section 3 are the same, but

1. the GS2 header on the client's first message is excluded when
OAUTH is used as a GSS-API mechanism, and

2. initial context token header is prefixed to the client's first
authentication message (context token), as described in Section
3.1 of RFC 2743,

The GSS-API mechanism OID for OAuth is [[TBD: IANA]].

OAuth 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, as discussed in
[RFC6125].

The OAuth mechanism does 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 supports 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.

5. Examples

These example illustrate exchanges between an IMAP client and an IMAP
server.

5.1. Successful Bearer Token Exchange

This example shows a successful OAuth 2.0 bearer token exchange with
an initial client response. Note that line breaks are inserted for
readability.

S: * IMAP4rev1 Server Ready
C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8gSFRUUC8xLjENCkhvc3Q6IGltYXAuZXhhbXBs
ZS5jb20NCkF1dGhvcml6YXRpb246IEJFQVJFUiAidkY5ZGZ0NHFtVGMyTnZiM1J
sY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09Ig0KDQo= aG9zdD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMB
YXV0aD1CRUFSRVIgdkY5ZGZ0NHFtVGMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVk
yOXRDZz09AQE=
S: +
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:

GET / HTTP/1.1
Host: imap.example.com
Authorization: BEARER "vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg=="

host=server.example.com^Aport=143^A
auth=BEARER "vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg=="^A^A

The line containing just a "+" and a space is an empty response from
the server. This response contains discovery error information, and in the
success case no discovery information is necessary so the error response is empty. Like other messages, and
in accordance with the IMAP SASL binding, the empty response is
base64-encoded.

5.2. MAC Authentication with Channel Binding

This example shows a channel binding failure. The example sends the
same request as above, but in the context of an OAUTH-PLUS exchange
the channel binding information is missing. Note that line breaks
are inserted for readability.

S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE MAC R0VUIC8/Y2JkYXRhPSJTRzkzSUdKcFp5QnBjeUJoSUZSTVV5Q
m1hVzVoYkNCdFpYTnpZV2RsUHdvPSIgSFRUUC8xLjENCkhvc3Q6IHNlcnZlci5leGFtcG
xlLmNvbQ0KVXNlcjogdXNlckBleGFtcGxlLmNvbQ0KQXV0aG9yaXphdGlvbjogTUFDIHR
va2VuPSJoNDgwZGpzOTNoZDgiLHRpbWVzdGFtcD0iMTM3MTMxMjAwIixub25jZT0iZGo4
M2hzOXMiLHNpZ25hdHVyZT0iV1c5MUlHMTFjM1FnWW1VZ1ltOXlaV1F1SUFvPSINCg0K aG9zdD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0a
D1NQUMgdG9rZW49Img0ODBkanM5M2hkOCIsdGltZXN0YW1wPSIxMzcxMzEyMDAiLG5vbm
NlPSJkajgzaHM5cyIsc2lnbmF0dXJlPSJZVFZqeU5TdWpZczFXc0R1ckZudkZpNEpLNm8
9IgFjYmRhdGE9U0c5M0lHSnBaeUJwY3lCaElGUk1VeUJtYVc1aGJDQnRaWE56WVdkbFB3
bz0BAQ==
S: +
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:

GET /?cbdata="SG93IGJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=" HTTP/1.1
Host: server.example.com
User: user@example.com
Authorization: MAC token="h480djs93hd8",timestamp="137131200",
nonce="dj83hs9s",signature="WW91IG11c3QgYmUgYm9yZWQuIAo="

-
host=server.example.com^A
port=143^A
auth=MAC token="h480djs93hd8",timestamp="137131200",nonce="dj83hs9s",
signature="YTVjyNSujYs1WsDurFnvFi4JK6o="^A
cbdata=SG93IGJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=^A^A

The line containing just a "+" and a space is an empty response from
the server. This response contains discovery information, and in the
success case no discovery information is necessary so the response is
empty. Like other messages, and in accordance with the IMAP SASL
binding, the empty response is base64-encoded.

5.3. Failed Exchange

This example shows a failed exchange because of the empty
Authorization header, which is how a client can query for discovery
information. the needed
scope. Note that line breaks are inserted for readability.

S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8gSFRUUC8xLjENClVzZXI6IHNjb290ZXJAYW
x0YXZpc3RhLmNvbQ0KSG9zdDogaW1hcC55YWhvby5jb20NCkF1dGhlbnRpY2F0ZT
ogDQoNCg== aG9zdD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xND
MBYXV0aD0BAQ==
S: + SFRUUC8xLjEgNDAxIFVuYXV0aG9yaXplZA0KV1dXLUF1dGhlbnRpY2F0ZTogQk
VBUkVSIHJlYWxtPSJleGFtcGxlLmNvbSINCkxpbms6IDxodHRwczovL2xvZ2luLn
lhaG9vLmNvbS9vYXV0aD4gcmVsPSJvYXV0aDItYXV0aGVudGljYXRvciIgIA0KTG
luazogPGh0dHBzOi8vbG9naW4ueWFob28uY29tL29hdXRoPiByZWw9Im91YXRoMi
10b2tlbiINCg0K ewoic3RhdHVzIjoiNDAxIiwKInNjb3BlIjoiZXhhbXBsZV9zY29wZSIKfQo=
S: t1 NO SASL authentication failed

The decoded initial client response is:

GET / HTTP/1.1
User: alice@example.com
Host: imap.example.com
Authorization:

host=server.example.com^Aport=143^Aauth=^A^A

The decoded server discovery error response is:

HTTP/1.1 401 Unauthorized
WWW-Authenticate: BEARER realm="example.com"
Link: <https://login.example.com/oauth> rel="oauth2-authenticator"
Link: <https://login.example.com/oauth> rel="oauth2-token"

{
"status":"401",
"scope":"example_scope"
}

5.4. Failed Channel Binding

This example shows a channel binding failure in a discovery an empty request.
The channel binding information is empty. Note that line breaks are
inserted for readability.

S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8/Y2JkYXRhPSIiIEhUVFAvMS4xDQpVc2VyOi
BhbGljZUBleGFtcGxlLmNvbQ0KSG9zdDogaW1hcC5leGFtcGxlLmNvbQ0KQXV0aG
9yaXphdGlvbjoNCg0K aG9zdD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xND
MBYXV0aD0BY2JkYXRhPQEB
S: + SFRUUC8xLjEgNDEyIFByZWNvbmRpdGlvbiBGYWlsZWQNCg0KDQo= ewoic3RhdHVzIjoiNDEyIiwKInNjb3BlIjoiZXhhbXBsZV9zY29wZSIKfQ==
S: t1 NO SASL authentication failed

The decoded initial client response is:

GET /?cbdata="" HTTP/1.1
User: alice@example.com
Host: imap.example.com
Authorization:

host=server.example.com^Aport=143^Aauth=^Acbdata=^A^A

The decoded server response is:

HTTP/1.1 412 Precondition Failed

{
"status":"412",
"scope":"example_scope"
}

6. Security Considerations

This mechanism does not provide a security layer, but does provide a
provision for channel binding. The OAuth 2 specification
[I-D.ietf-oauth-v2] allows for a variety of usages, and the security
properties of these profiles vary. The usage of bearer tokens, for
example, provide security features similar to cookies. Applications
using this mechanism SHOULD exercise the same level of care using
this mechanism as they would in using the SASL PLAIN mechanism. In
particular, TLS 1.2 or an equivalent secure channel MUST be
implemented and its usage is RECOMMENDED.

Channel binding in this mechanism has different properties based on
the authentication scheme used. Channel binding to TLS with a bearer
token provides only a binding to the TLS layer. Authentication
schemes like MAC tokens have can implement a signature over the channel
binding information. These provide additional protection against a
man in the middle attacks, and the MAC authorization header is bound
to the channel and only valid in that context.

It is possible that SASL will be authenticating a connection and the
life of that connection may outlast the life of the token used to
authenticate 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.

An OAuth credential is not equivalent to the password or primary
account credential. There are protocols like XMPP that allow actions
like change password. The server SHOULD ensure that actions taken in
the authenticated channel are appropriate to the strength of the
presented credential.

It is possible for an application server running on Evil.example.com
to tell a client to request a token from Good.example.org. A client
following these instructions will pass a token from Good to Evil.
This is by design, since it is possible that Good and Evil are merely
names, not descriptive, and that this is an innocuous activity
between cooperating two servers taken in different domains. For instance,
a site might operate their authentication service in-house, but
outsource their mail systems
the authenticated channel are appropriate to an external entity. the strength of the
presented credential.

Tokens have a lifetime associated with them. Reducing both the lifetime
of a token provides security benefits in case that tokens leak. In
addition a previously obtained 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. IANA Considerations

7.1. SASL Registration

The IANA is requested to register the following SASL profile:

SASL mechanism profile: OAUTH

Security Considerations: See this document

Published Specification: See this document

For further information: Contact the authors of this document.

Owner/Change controller: the IETF

Note: None

The IANA is requested to register the following SASL profile:

SASL mechanism profile: OAUTH-PLUS

Security Considerations: See this document

Published Specification: See this document

For further information: Contact the authors of this document.

Owner/Change controller: the IETF

Note: None

7.2. GSS-API Registration

IANA is further requested to assign an OID for this GSS mechanism 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.

7.3. Link Type Registration

Pursuant to [RFC5988] The following link type registrations [[will
be]] registered by mail to link-relations@ietf.org.

7.3.1. OAuth 2 Authentication Endpoint
o Relation Name: oauth2-authenticator

o Description: An OAuth 2.0 authentication endpoint.

o Reference:

o Notes: This link type indicates an OAuth 2.0 authentication
endpoint that can be used for user authentication/authorization
for the endpoint providing the link.

o Application Data: [optional]

7.3.2. OAuth 2 Token Endpoint

o Relation Name: oauth2-token

o Description: The OAuth token endpoint used to get tokens for
access.

o Reference:

o Notes: The OAuth 2.0 token endpoint to be used for obtaining
tokens to access the endpoint providing the link.

o Application Data: This link type has one link-extension "grant-
types", which is the OAuth 2.0 grant types that can be used at the
token endpoint to obtain a token. This is not an exclusive list,
it provides a hint to the application of what SHOULD be valid. A
token endpoint MAY support additional grant types not advertised
by a resource endpoint.

7.3.3. OAuth 1.0a Request Initiation Endpoint

o Relation Name: oauth-initiate

o Description: The OAuth 1.0a request initiation endpoint used to
get tokens for access.

o Reference:

o Notes: mechanism profile: OAUTH

Security Considerations: See this document

Published Specification: See this document

For further information: Contact the authors of this document.

Owner/Change controller: the IETF

Note: None

The OAuth 1.0a endpoint used IANA is requested to initiate register the sequence, following SASL profile:

SASL mechanism profile: OAUTH-PLUS

Security Considerations: See this
temporary request is what document

Published Specification: See this document

For further information: Contact the user approves to grant access to authors of this document.

Owner/Change controller: the
resource.

o Application Data:

7.3.4. OAuth 1.0a Authorization Endpoint

o Relation Name: oauth-authorize

o Description: The OAuth 1.0a authorization endpoint used IETF

Note: None

7.2. GSS-API Registration

IANA is further requested to approve assign an access request.

o Reference:

o Notes:

o Application Data:

7.3.5. OAuth 1.0a Token Endpoint

o Relation Name: oauth-token

o Description: The OAuth 1.0a token endpoint used to get tokens OID for
access.

o Reference:

o Notes:

o Application Data: this GSS mechanism 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.

8. Appendix A -- Document History

[[ to be removed by RFC editor before publication as an RFC ]]

-04

o Editorial clean-up and text in introduction improved.

o Added GSS-API support

-03

o Fixing channel binding, not tls-unique specific. Also defining
how the CB data is properly generated.

o Various small editorial changes and embarassing spelling fixes.

-02

-01

o Filling Ripping out Channel Binding

o Added text clarifying how discovery. Changed to bind refer to the 2 kinds I-D.jones-appsawg-
webfinger instead of SASL
identities.

-01 WF and SWD older drafts.

o Bringing this into line with draft 12 of the core spec, Replacing HTTP as the bearer
token spec, message format and references the MAC token spec adjusted all examples.

-00

o Changing discovery over to using the Link header construct from
RFC5988. Renamed draft into proper IETF naming format now that it's
adopted.

o Added the seeds of channel binding. Minor fixes.

-00

o Initial revision

9. References

9.1. Normative References

[I-D.ietf-oauth-v2]
Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth
2.0 Authorization Protocol", draft-ietf-oauth-v2-22 Framework", draft-ietf-oauth-v2-26 (work
in progress), September 2011. May 2012.

[I-D.ietf-oauth-v2-bearer]
Jones, M., Hardt, D., and D. Recordon, "The OAuth 2.0
Authorization Protocol: Bearer Tokens",
draft-ietf-oauth-v2-bearer-14
draft-ietf-oauth-v2-bearer-19 (work in progress),
November 2011.
April 2012.

[I-D.ietf-oauth-v2-http-mac]
Hammer-Lahav, E., Barth, A., and B. Adida, "HTTP Authentication: MAC Access
Authentication",
draft-ietf-oauth-v2-http-mac-00 draft-ietf-oauth-v2-http-mac-01 (work in
progress),
May 2011. February 2012.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.

[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.

[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.

[RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, September 2001.

[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.

[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.

[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, November 2007.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.

[RFC5801] Josefsson, S. and N. Williams, "Using Generic Security
Service Application Program Interface (GSS-API) Mechanisms
in Simple Authentication and Security Layer (SASL): The
GS2 Mechanism Family", RFC 5801, July 2010.

[RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
April 2010.

[RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings
for TLS", RFC 5929, July 2010.

[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.

[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.

9.2. Informative References

[I-D.hammer-hostmeta]
Hammer-Lahav, E. and B. Cook, "Web Host Metadata",
draft-hammer-hostmeta-17 (work in progress),
September 2011.

[I-D.jones-simple-web-discovery]

[I-D.jones-appsawg-webfinger]
Jones, M. P., Salgueiro, G., and Y. Goland, "Simple Web Discovery (SWD)",
draft-jones-simple-web-discovery-01 J. Smarr, "WebFinger",
draft-jones-appsawg-webfinger-05 (work in progress),
July 2011.
May 2012.

[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.

Authors' Addresses

William Mills
Yahoo! Inc.

Phone:
Email: wmills@yahoo-inc.com

Tim Showalter
Yahoo! Inc.

Phone:
Email: timshow@yahoo-inc.com tjs@psaux.com

Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland

Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at