A SASL and GSS-API Mechanism for OAuth
draft-ietf-kitten-sasl-oauth-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7628.
Expired & archived
|
|
|---|---|---|---|
| Authors | William Mills , Tim Showalter , Hannes Tschofenig | ||
| Last updated | 2012-05-16 (Latest revision 2011-11-13) | ||
| Replaces | draft-mills-kitten-sasl-oauth | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 7628 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-kitten-sasl-oauth-00
KITTEN W. Mills
Internet-Draft T. Showalter
Intended status: Standards Track Yahoo! Inc.
Expires: May 17, 2012 H. Tschofenig
Nokia Siemens Networks
November 14, 2011
A SASL and GSS-API Mechanism for OAuth
draft-ietf-kitten-sasl-oauth-00.txt
Abstract
OAuth enables a third-party application to obtain limited access to a
protected resource, either on behalf of a resource owner by
orchestrating an approval interaction, or by allowing the third-party
application to obtain access on its own behalf.
This document defines how an application client uses 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. 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Mills, et al. Expires May 17, 2012 [Page 1]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
This Internet-Draft will expire on May 17, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Mills, et al. Expires May 17, 2012 [Page 2]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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 in OAUTH-PLUS . . . . . . . . . . . . . . 9
3.3. Server's Response . . . . . . . . . . . . . . . . . . . . 9
3.4. Mapping to SASL Identities . . . . . . . . . . . . . . . . 10
3.5. Discovery Information . . . . . . . . . . . . . . . . . . 10
3.6. Use of Signature Type Authorization . . . . . . . . . . . 12
4. GSS-API OAuth Mechanism Specification . . . . . . . . . . . . 14
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Successful Bearer Token Exchange . . . . . . . . . . . . . 15
5.2. MAC Authentication with Channel Binding . . . . . . . . . 15
5.3. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 16
5.4. Failed Channel Binding . . . . . . . . . . . . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 19
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
8. Appendix A -- Document History . . . . . . . . . . . . . . . . 22
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 23
9.2. Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
Mills, et al. Expires May 17, 2012 [Page 3]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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
Mills, et al. Expires May 17, 2012 [Page 4]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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
Mills, et al. Expires May 17, 2012 [Page 5]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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 optional discovery exchange steps that may happen
before the OAuth 2.0 protocol exchange messages in steps (A)-(D) are
executed. Steps (E) and (F) also 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 -------->| | |SASL/
| | | | |GSS-
| |<-(F)---- Protected Resource -----| | |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].
Mills, et al. Expires May 17, 2012 [Page 6]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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.
Mills, et al. Expires May 17, 2012 [Page 7]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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 for SASL
while "OAUTH-PLUS" provides a semantic similar to OAuth MAC
authentication by utilizing a channel binding mechanism [RFC5056].
3.1. 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 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 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:
Mills, et al. Expires May 17, 2012 [Page 8]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
User (OPTIONAL): Contains the user identifier being
authenticated, and is provided to allow correct discovery
information to be returned.
Host (REQUIRED): 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): 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
Mills, et al. Expires May 17, 2012 [Page 9]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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 to token which equates to the SASL authentication
identity, and is authenticated using the shared secret. The
authorization identity in the OAuth 1.0a case is carried in the token
(per the requirement above), which SHOULD validated independently.
The server MAY use a consumer key or other comparable identity in the
OAuth authorization scheme as the SASL authentication identity. If
an appropriate authentication identity is not available the server
MUST 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 the discovery information MUST be for that user.
Discovery information is provided by the server to the client to
allow a client to discover the appropriate OAuth authentication and
token endpoints. The client then uses that information to obtain the
access token needed for OAuth authentication. The client SHOULD
cache and re-use the user specific discovery information for service
endpoints.
Discovery information makes use of both the WWW-Authenticate header
as defined in HTTP Authentication: Basic and Digest Access
Authentication [RFC2617] and Link headers as defined in [RFC5988].
Mills, et al. Expires May 17, 2012 [Page 10]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
The following elements are defined for discovery information:
WWW-Authenticate A WWW-Authenticate header for each authentication
scheme supported by the server. Authentication scheme names are
case insensitive. The following [RFC2617] authentication
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 for the resource.
oauth2-authenticator An [RFC5988] Link header specifying the
[I-D.ietf-oauth-v2] authentication endpoint. This link has an
OPTIONAL link-extension "scheme", if included this link applies
ONLY to the specified scheme.
oauth2-token An [RFC5988] Link header specifying the
[I-D.ietf-oauth-v2] token endpoint. This link has an OPTIONAL
link-extension "scheme", if included this link applies ONLY to the
specified scheme.
oauth-initiate (Optional) An [RFC5988] Link header specifying the
OAuth1.0a [RFC5849] initiation endpoint. The server MUST send
this if "OAuth" is included in the supported list of HTTP
authentication schemes for the server.
oauth-authorize (Optional) An [RFC5988] Link header specifying the
OAuth1.0a [RFC5849] authentication endpoint. The server MUST send
this if "OAuth" is included in the supported list of HTTP
authentication schemes for the server.
oauth-token (Optional) An [RFC5988] Link header specifying the
OAuth1.0a [RFC5849] token endpoint. The server MUST send this if
"OAuth" is included in the supported list of HTTP authentication
schemes for the server. This link type has one link-extension
"grant-types" which is a space separated list of the OAuth 2.0
grant types that can be used at the token endpoint to obtain a
token.
Usage of the URLs provided in the discovery information is defined in
the relevant specifications. If the server supports multiple
authenticators the discovery information returned for unknown users
MUST be consistent with the discovery information for known users to
prevent user enumeration. The OAuth 2.0 specification
[I-D.ietf-oauth-v2] supports multiple types of authentication schemes
and the server MUST specify at least one supported authentication
scheme in the discovery information. The server MAY support multiple
Mills, et al. Expires May 17, 2012 [Page 11]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
schemes and MAY support schemes not listed in the discovery
information.
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 be defined by
the resource owner and provided in service documentation (which is
beyond the scope of this memo).
3.6. 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 an HTTP style format specifically to support signature type
authentication, but this is extremely limited. The HTTP style
request is limited to a path of "/". This mechanism is in the SASL
model, but is designed so that no changes are needed if there is a
revision of SASL which supports more specific resource authorization,
e.g. IMAP access to a specific folder or FTP access limited to a
specific directory.
Using the example in the 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 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 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:
Mills, et al. Expires May 17, 2012 [Page 12]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
h480djs93hi8\n
137131200\n
dj83hs9s\n
\n
GET\n
server.example.com\n
143\n
/\n
\n
Mills, et al. Expires May 17, 2012 [Page 13]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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.
Mills, et al. Expires May 17, 2012 [Page 14]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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=
S: +
S: t1 OK SASL authentication succeeded
As required by IMAP [RFC3501], the payloads are base64-encoded. The
decoded initial client response is:
GET / HTTP/1.1
Host: imap.example.com
Authorization: BEARER "vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg=="
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.
5.2. 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.
Mills, et al. Expires May 17, 2012 [Page 15]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE MAC R0VUIC8/Y2JkYXRhPSJTRzkzSUdKcFp5QnBjeUJoSUZSTVV5Q
m1hVzVoYkNCdFpYTnpZV2RsUHdvPSIgSFRUUC8xLjENCkhvc3Q6IHNlcnZlci5leGFtcG
xlLmNvbQ0KVXNlcjogdXNlckBleGFtcGxlLmNvbQ0KQXV0aG9yaXphdGlvbjogTUFDIHR
va2VuPSJoNDgwZGpzOTNoZDgiLHRpbWVzdGFtcD0iMTM3MTMxMjAwIixub25jZT0iZGo4
M2hzOXMiLHNpZ25hdHVyZT0iV1c5MUlHMTFjM1FnWW1VZ1ltOXlaV1F1SUFvPSINCg0K
S: +
S: t1 OK SASL authentication succeeded
As required by IMAP [RFC3501], the payloads are base64-encoded. The
decoded initial client response 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="
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. 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==
S: + SFRUUC8xLjEgNDAxIFVuYXV0aG9yaXplZA0KV1dXLUF1dGhlbnRpY2F0ZTogQk
VBUkVSIHJlYWxtPSJleGFtcGxlLmNvbSINCkxpbms6IDxodHRwczovL2xvZ2luLn
lhaG9vLmNvbS9vYXV0aD4gcmVsPSJvYXV0aDItYXV0aGVudGljYXRvciIgIA0KTG
luazogPGh0dHBzOi8vbG9naW4ueWFob28uY29tL29hdXRoPiByZWw9Im91YXRoMi
10b2tlbiINCg0K
S: t1 NO SASL authentication failed
The decoded initial client response is:
Mills, et al. Expires May 17, 2012 [Page 16]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
GET / HTTP/1.1
User: alice@example.com
Host: imap.example.com
Authorization:
The decoded server discovery 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"
5.4. Failed Channel Binding
This example shows a channel binding failure in a discovery 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
S: + SFRUUC8xLjEgNDEyIFByZWNvbmRpdGlvbiBGYWlsZWQNCg0KDQo=
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:
The decoded server response is:
HTTP/1.1 412 Precondition Failed
Mills, et al. Expires May 17, 2012 [Page 17]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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 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 in different domains. For instance,
a site might operate their authentication service in-house, but
outsource their mail systems to an external entity.
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.
Mills, et al. Expires May 17, 2012 [Page 18]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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
Mills, et al. Expires May 17, 2012 [Page 19]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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: The OAuth 1.0a endpoint used to initiate the sequence, this
temporary request is what the user approves to grant access to the
resource.
o Application Data:
Mills, et al. Expires May 17, 2012 [Page 20]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
7.3.4. OAuth 1.0a Authorization Endpoint
o Relation Name: oauth-authorize
o Description: The OAuth 1.0a authorization endpoint used to approve
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 for
access.
o Reference:
o Notes:
o Application Data:
Mills, et al. Expires May 17, 2012 [Page 21]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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
o Filling out Channel Binding
o Added text clarifying how to bind to the 2 kinds of SASL
identities.
-01
o Bringing this into line with draft 12 of the core spec, the bearer
token spec, and references the MAC token spec
o Changing discovery over to using the Link header construct from
RFC5988.
o Added the seeds of channel binding.
-00
o Initial revision
Mills, et al. Expires May 17, 2012 [Page 22]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
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 (work
in progress), September 2011.
[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 (work in progress),
November 2011.
[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 (work in progress),
May 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 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.
[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.
Mills, et al. Expires May 17, 2012 [Page 23]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
[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]
Jones, M. and Y. Goland, "Simple Web Discovery (SWD)",
draft-jones-simple-web-discovery-01 (work in progress),
July 2011.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
Mills, et al. Expires May 17, 2012 [Page 24]
Internet-Draft A SASL/GSS-API Mechanism for OAuth November 2011
Authors' Addresses
William Mills
Yahoo! Inc.
Phone:
Email: wmills@yahoo-inc.com
Tim Showalter
Yahoo! Inc.
Phone:
Email: timshow@yahoo-inc.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
Mills, et al. Expires May 17, 2012 [Page 25]