A set of SASL and GSS-API Mechanisms for OAuth
draft-ietf-kitten-sasl-oauth-09
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.
|
|
|---|---|---|---|
| Authors | William Mills , Tim Showalter , Hannes Tschofenig | ||
| Last updated | 2012-12-17 | ||
| Replaces | draft-mills-kitten-sasl-oauth | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | In WG Last Call | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 7628 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
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| Send notices to | (None) |
draft-ietf-kitten-sasl-oauth-09
KITTEN W. Mills
Internet-Draft Yahoo! Inc.
Intended status: Standards Track T. Showalter
Expires: June 20, 2013
H. Tschofenig
Nokia Siemens Networks
December 17, 2012
A set of SASL and GSS-API Mechanisms for OAuth
draft-ietf-kitten-sasl-oauth-09
Abstract
OAuth enables a third-party application to obtain limited access to a
protected resource, either on behalf of a resource owner by
orchestrating an approval interaction, or by allowing the third-party
application to obtain access on its own behalf.
This document defines how an application client uses credentials
obtained via OAuth over the Simple Authentication and Security Layer
(SASL) or the Generic Security Service Application Program Interface
(GSS-API) to access a protected resource at a resource serve.
Thereby, it enables schemes defined within the OAuth framework for
non-HTTP-based application protocols.
Clients typically store the user's long-term credential. This does,
however, lead to significant security vulnerabilities, for example,
when such a credential leaks. A significant benefit of OAuth for
usage in those clients is that the password is replaced by a token.
Tokens typically provided limited access rights and can be managed
and revoked separately from the user's long-term credential
(password).
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."
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This Internet-Draft will expire on June 20, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. OAuth SASL Mechanism Specifications . . . . . . . . . . . . . 8
3.1. Initial Client Response . . . . . . . . . . . . . . . . . 9
3.1.1. Reserved Key/Values . . . . . . . . . . . . . . . . . 10
3.1.2. Use of the gs2-header . . . . . . . . . . . . . . . . 10
3.2. Server's Response . . . . . . . . . . . . . . . . . . . . 10
3.2.1. OAuth Identifiers in the SASL Context . . . . . . . . 11
3.2.2. Server Response to Failed Authentication . . . . . . . 11
3.2.3. Completing an Error Message Sequence . . . . . . . . . 12
3.3. OAuth Access Token Types using Digital Signatures and
Keyed Message Digests . . . . . . . . . . . . . . . . . . 12
3.4. Channel Binding . . . . . . . . . . . . . . . . . . . . . 13
4. GSS-API OAuth Mechanism Specification . . . . . . . . . . . . 14
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Successful Bearer Token Exchange . . . . . . . . . . . . . 16
5.2. OAuth 1.0a Authorization with Channel Binding . . . . . . 17
5.3. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 18
5.4. Failed Channel Binding . . . . . . . . . . . . . . . . . . 19
5.5. SMTP Example of a Failed Negotiation . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7. Internationalization Considerations . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
8.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 23
8.2. GSS-API Registration . . . . . . . . . . . . . . . . . . . 24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.1. Normative References . . . . . . . . . . . . . . . . . . . 25
9.2. Informative References . . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowlegements . . . . . . . . . . . . . . . . . . . 28
Appendix B. Document History . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
OAuth [RFC6749] enables a third-party application to obtain limited
access to a protected resource, either on behalf of a resource owner
by orchestrating an approval interaction, or by allowing the third-
party application to obtain access on its own behalf. The core OAuth
2.0 specification [RFC6749] does not define the interaction between
the client and the resource server with the access to a protected
resource using an Access Token. This functionality is described in
separate specifications, for example bearer tokens [RFC6750], OAuth
2.0 MAC tokens [I-D.ietf-oauth-v2-http-mac]. OAuth 1.0a [RFC5849],
the predecessor of OAuth 2.0, has a similar design. The main use
cases for OAuth 2.0 and OAuth 1.0 have so far focused on an HTTP-
based environment only.
Figure 1 shows the abstract message flow as shown in Figure 1 of
OAuth 2.0 [RFC6749].
+--------+ +---------------+
| |--(A)- Authorization Request ->| Resource |
| | | Owner |
| |<-(B)-- Authorization Grant ---| |
| | +---------------+
| |
| | +---------------+
| |--(C)-- Authorization Grant -->| Authorization |
| Client | | Server |
| |<-(D)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(E)----- Access Token ------>| Resource |
| | | Server |
| |<-(F)--- Protected Resource ---| |
+--------+ +---------------+
Figure 1: Abstract OAuth 2.0 Protocol Flow
This document takes advantage of the OAuth protocol and its
deployment base to provide a way to use SASL [RFC4422] as well as the
GSS-API [RFC2743] to gain access to resources when using non-HTTP-
based protocols, such as the Internet Message Access Protocol (IMAP)
[RFC3501] and SMTP [RFC5321], which is what this memo uses in the
examples.
The Simple Authentication and Security Layer (SASL) is a framework
for providing authentication and data security services in
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connection-oriented protocols via replaceable mechanisms. It
provides a structured interface between protocols and mechanisms.
The resulting framework allows new protocols to reuse existing
mechanisms and allows old protocols to make use of new mechanisms.
The framework also provides a protocol for securing subsequent
protocol exchanges within a data security layer.
The Generic Security Service Application Program Interface (GSS-API)
[RFC2743] provides a framework for applications to support multiple
authentication mechanisms through a unified interface.
This document defines SASL mechanisms for OAuth, and it conforms to
the new bridge between SASL and the GSS-API called GS2 [RFC5801].
This means that this document defines both SASL and GSS-API
mechanisms. Implementers may be interested in either the SASL, the
GSS-API, or even both mechanisms. To facilitate these two variants,
the description has been split into two parts, one part that provides
normative references for those interested in the SASL OAuth mechanism
(see Section 3), and a second part for those implementers that wish
to implement the GSS-API portion (see Section 4).
When OAuth is integrated into SASL and the GSS-API the high-level
steps are as follows:
(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,
indicates a successful authentication.
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Steps (E) and (F) are not defined in [RFC6749] and are the main
functionality specified within this document. Consequently, the
message exchange shown in Figure 2 is the result of this
specification. The client will generally need to determine the
authentication endpoints (and perhaps the service endpoints) before
the OAuth 2.0 protocol exchange messages in steps (A)-(D) are
executed. The discovery of the resource owner and authorization
server endpoints is outside the scope of this specification. The
client must discover those endpoints using a discovery mechanisms
such as Webfinger using host-meta [I-D.ietf-appsawg-webfinger]. In
band discovery is not tenable if clients support the OAuth 2.0
password grant. Once credentials are obtained the client proceeds to
steps (E) and (F) defined in this specification.
----+
+--------+ +---------------+ |
| |--(A)-- Authorization Request --->| Resource | |
| | | Owner | |Plain
| |<-(B)------ Access Grant ---------| | |OAuth
| | +---------------+ |2.0
| | |
| | Client Credentials & +---------------+ |
| |--(C)------ Access Grant -------->| Authorization | |
| Client | | Server | |
| |<-(D)------ Access Token ---------| | |
| | (w/ Optional Refresh Token) +---------------+ |
| | ----+
| | ----+
| | +---------------+ |
| | | | |OAuth
| |--(E)------ Access Token -------->| Resource | |over
| | | Server | |SASL/
| |<-(F)---- Protected Resource -----| | |GSS-
| | | | |API
+--------+ +---------------+ |
----+
Figure 2: OAuth SASL Architecture
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The reader is assumed to be familiar with the terms used in the OAuth
2.0 specification [RFC6749].
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. Line breaks have been inserted for readability.
Note that the IMAP SASL specification requires base64 encoding, see
Section 4 of [RFC4648], not this memo.
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3. OAuth SASL Mechanism Specifications
SASL is used as an authentication framework in a variety of
application layer protocols. This document defines the following
SASL mechanisms for usage with OAuth:
OAUTHBEARER: Authorization using OAuth 2.0 bearer tokens as
described in [RFC6750].
OAUTH10A: Authorization using OAuth 1.0a MAC tokens (using the
HMAC-SHA1 keyed message digest) as described in Section 3.4.2
of [RFC5849].
OAUTH10A-PLUS: Adds channel binding [RFC5056] capability to
OAUTH10A for protection against man-in-the-middle attacks.
New extensions may be defined to add additional OAuth Access Token
Types. Such a new SASL OAuth mechanism can be added by simply
registering the new name(s) and citing this specification for the
further definition. New channel binding enabled "-PLUS" mechanisms
defined in this way MUST include message integrity protection. A
newly defined mechanism would also need to register a new GS2 OID.
These mechanisms are client initiated and lock-step, the server
always replying to a client message. In the case where the client
has and correctly uses a valid token the flow is:
o Client sends a valid and correct initial client response.
o Server responds with a successful authentication.
In the case where authorization fails the server sends an error
result, then client MUST then send an additional message to the
server in order to allow the server to finish the exchange. Some
protocols and common SASL implementations do not support both sending
a SASL message and finalizing a SASL negotiation, the additional
client message in the error case deals with this problem. This
exchange is:
o Client sends an invalid initial client response.
o Server responds with an error message.
o Client sends a dummy client response.
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o Server fails the authentication.
3.1. Initial Client Response
Client responses are a key/value pair sequence. The initial client
response includes a gs2-header as defined in GS2 [RFC5801], which
carries the authorization ID. These key/value pairs carry the
equivalent values from an HTTP context in order to be able to
complete an OAuth style HTTP authorization. Unknown key/value pairs
MUST be ignored by the server. The ABNF [RFC5234] syntax is:
kvsep = %x01
key = 1*ALPHA
value = *(VCHAR / SP / HTAB / CR / LF )
kvpair = key "=" value kvsep
client_resp = 0*kvpair kvsep
;; gs2-header = As defined in GSS-API
initial_client_resp = gs2-header kvsep client_resp
The following key/value pairs are defined in the client response:
auth (REQUIRED): The payload of the HTTP Authorization header for
an equivalent HTTP OAuth authorization.
host: Contains the host name to which the client connected.
port: Contains the port number represented as a decimal positive
integer string without leading zeros to which the client
connected.
qs: The HTTP query string. In non-channel binding mechanisms
this is reserved, the client SHOUD NOT send it, and has the
default value of "". In "-PLUS" variants this carries a single
key value pair "cbdata" for the channel binding data payload
formatted as an HTTP query string.
For OAuth Access Token Types that use digital signatures or keyed
message digests the client MUST send host and port number key/values,
and the server MUST fail an authorization request requiring
signatures or keyed message digests that do not have host and port
values. For authorization schemes that require a URI scheme as part
of the data being signed "http" is always used. In OAuth 1.0a for
example, the so-called signature base string calculation includes the
reconstructed HTTP URL.
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3.1.1. Reserved Key/Values
In these mechanisms values for path, query string and post body are
assigned default values. OAuth authorization schemes MAY define
usage of these in the SASL context and extend this specification.
For OAuth Access Token Types that use request signatures the default
values MUST be used unless explicit values are provided in the client
response. The following key values are reserved for future use:
mthd (RESERVED): HTTP method for use in signatures, the default
value is "POST".
path (RESERVED): HTTP path data, the default value is "/".
post (RESERVED): HTTP post data, the default value is "".
3.1.2. Use of the gs2-header
The OAuth scheme related mechanisms are also GSS-API mechanisms, see
Section 4 for further detail. The gs2-header is used as follows:
o The "gs2-nonstd-flag" MUST NOT be present.
o The "gs2-authzid" carries the authorization identity as specified
in [RFC5801]. If present the application MUST determine whether
access is granted for the identity asserted in the OAuth
credential, if it does not the server MUST fail the negotiation.
In the non "-PLUS" mechanisms the "gs2-cb-flag" MUST be set to "n"
because channel-binding [RFC5056] data is not expected. In the
OAUTH10A-PLUS mechanism (or other -PLUS variants based on this
specification) the "gs2-cb-flag" MUST be set appropriately by the
client.
3.2. Server's Response
The server validates the response per the specification for the OAuth
Access Token Types used. If the OAuth Access Token Type utilizes a
digital signature or a keyed message digest of the request parameters
then the client must provide a client response that satisfies the
data requirements for the scheme in use.
In a "-PLUS" mechanism the server examines the channel binding data,
extracts the channel binding unique prefix, and extracts the raw
channel biding data based on the channel binding type used. It then
computes it's own copy of the channel binding payload and compares
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that to the payload sent by the client in the cbdata key/value.
Those two must be equal for channel binding to succeed.
The server responds to a successfully verified client message by
completing the SASL negotiation. The authenticated identity reported
by the SASL mechanism is the identity securely established for the
client with the OAuth credential. The application, not the SASL
mechanism, based on local access policy determines whether the
identity reported by the mechanism is allowed access to the requested
resource. Note that the semantics of the authz-id is specified by
the SASL framework [RFC4422].
3.2.1. OAuth Identifiers in the SASL Context
OAuth access tokens may carry the authenticated identifier of the
resource owner and client authentication provides the authenticated
identity of the client issuing the request to the resource server.
If both identities are needed by an application the developer will
need to provide a way to communicate that from the SASL mechanism
back to the application such as a GSS-API [RFC2743] named type like
GSS_C_NT_USER_NAME or a comparable newly defined GSS-API name type or
name attribute [RFC6680].
3.2.2. Server Response to Failed Authentication
For a failed authentication the server returns a JSON [RFC4627]
formatted error result, and fails the authentication. The error
result consists of the following values:
status (REQUIRED): The authorization error code. Valid error
codes are defined in the IANA [[need registry name]] registry
specified in the OAuth 2 core specification.
scope (OPTIONAL): An OAuth scope which is valid to access the
service. This may be empty which implies that unscoped tokens
are required, or a space separated list. Use of a space
separated list is NOT RECOMMENDED.
If the resource server provides a scope then the client MUST always
request scoped tokens from the token endpoint. If the resource
server provides no scope to the client then the client SHOULD presume
an empty scope (unscoped token) is needed.
If channel binding is in use and the channel binding fails the server
responds with a status code set to 412 to indicate that the channel
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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.
3.2.3. Completing an Error Message Sequence
Section 3.6 of [RFC4422] explicitly prohibits additional information
in an unsuccessful authentication outcome. Therefore, the error
message is sent in a normal message. The client MUST then send an
additional client response consisting of a single %x01 (control A)
character to the server in order to allow the server to finish the
exchange.
3.3. OAuth Access Token Types using Digital Signatures and Keyed
Message Digests
OAuth Access Token Types may use digital signatures or keyed message
digests. The client and the resource server need to perform a
cryptographic computation for integrity protection and data origin
authentication.
OAuth is designed for access to resources identified by URIs. SASL
is designed for user authentication, and has no facility for more
fine-grained access control. In this specification we require or
define default values for the data elements from an HTTP request
which allow the signature base string to be constructed properly.
The default HTTP path is "/" and the default post body is empty.
These atoms are defined as extension points so that no changes are
needed if there is a revision of SASL which supports more specific
resource authorization, e.g., IMAP access to a specific folder or FTP
access limited to a specific directory.
Using the example in the OAuth 1.0a specification as a starting
point, on an IMAP server running on port 143 and given the OAuth 1.0a
style authorization request (with %x01 shown as ^A and line breaks
added for readability) below:
n,a=user@example.com^A
host=example.com^A
user=user@example.com^A
port=143^A
auth=OAuth realm="Example",
oauth_consumer_key="9djdj82h48djs9d2",
oauth_token="kkk9d7dh3k39sjv7",
oauth_signature_method="HMAC-SHA1",
oauth_timestamp="137131201",
oauth_nonce="7d8f3e4a",
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oauth_signature="Tm90IGEgcmVhbCBzaWduYXR1cmU%3D"^A^A
The signature base string would be constructed per the OAuth 1.0
specification [RFC5849] with the following things noted:
o The method value is defaulted to POST.
o The scheme defaults to be "http", and any port number other than
80 is included.
o The path defaults to "/".
o The query string defaults to "".
In this example the signature base string with line breaks added for
readability would be:
POST&http%3A%2F%2Fexample.com:143%2F&oauth_consumer_key%3D9djdj82h4
8djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_method%3DHMAC-SH
A1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39sjv7
3.4. Channel Binding
The channel binding data is carried in the "qs" (query string) key
value pair formatted as a standard HTTP query parameter with the name
"cbdata". Channel binding requires that the channel binding data be
integrity protected end-to-end in order to protect against man-in-
the-middle attacks. All SASL OAuth mechanisms with a "-PLUS" postfix
MUST provide integrity protection. It should be noted that while the
Bearer Access Token Type mandates TLS it does not create keying
material at the application layer and is not suitable for use with
channel bindings.
The channel binding data is computed by the client based on it's
choice of preferred channel binding type. As specified in [RFC5056],
the channel binding information MUST start with the channel binding
unique prefix, followed by a colon (ASCII 0x3A), followed by a base64
encoded channel binding payload. The channel binding payload is the
raw data from the channel binding type. For example, if the client
is using tls-unique for channel binding then the raw channel binding
data is the TLS finished message as specified in Section 3.1 of
[RFC5929].
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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.
A SASL OAuth mechanism is also a GSS-API mechanism and the messages
described in Section 3 are the same with the following changes to the
GS2 related elements:
1. the GS2 header on the client's first message is excluded when
used as a GSS-API mechanism.
2. the initial context token header is prefixed to the client's
first authentication message (context token), as described in
Section 3.1 of RFC 2743,
The GSS-API mechanism OIDs are:
o OAUTHBEARER: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]
o OAUTH10A: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]
OAuth mechanims security contexts always have the mutual_state flag
(GSS_C_MUTUAL_FLAG) set to TRUE. OAuth supports credential
delegation, therefore security contexts may have the deleg_state flag
(GSS_C_DELEG_FLAG) set to either TRUE or FALSE.
The mutual authentication property of this mechanism relies on
successfully comparing the TLS server identity with the negotiated
target name. Since the TLS channel is managed by the application
outside of the GSS-API mechanism, the mechanism itself is unable to
confirm the name while the application is able to perform this
comparison for the mechanism. For this reason, applications MUST
match the TLS server identity with the target name using the
appropriate application profile, as discussed in [RFC6125]. For
example, when SASL OAuth is run over IMAP then the IMAP profile of
RFC 6125 is used.
OAuth mechanisms do not support per-message tokens or
GSS_Pseudo_random.
OAuth supports a standard generic name syntax for acceptors, such as
GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743], Section 4.1). These
service names MUST be associated with the "entityID" claimed by the
RP. OAuth mechanisms support only a single name type for initiators:
GSS_C_NT_USER_NAME. GSS_C_NT_USER_NAME is the default name type.
The query, display, and exported name syntaxes for OAuth principal
names are all the same. There is no OAuth-specific name syntax;
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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.
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5. Examples
These examples illustrate exchanges between an IMAP and SMTP clients
and servers.
Note to implementers: The SASL OAuth method names are case
insensitive. One example uses "Bearer" but that could as easily be
"bearer", "BEARER", or "BeArEr".
5.1. Successful Bearer Token Exchange
This example shows a successful OAuth 2.0 bearer token exchange.
Note that line breaks are inserted for readability.
S: * OK IMAP4rev1 Server Ready
C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX
J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV
GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE=
S: t1 OK SASL authentication succeeded
As required by IMAP [RFC3501], the payloads are base64-encoded. The
decoded initial client response (with %x01 represented as ^A and long
lines wrapped for readability) is:
n,a=user@example.com^Ahost=server.example.com^Aport=143^A
auth=Bearer vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg==^A^A
The same credential used in an SMTP exchange is shown below. Note
that line breaks are inserted for readability, and that the SMTP
protocol terminates lines with CR and LF characters (ASCII values
0x0D and 0x0A), these are not displayed explicitly in the example.
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[connection begins]
S: 220 mx.example.com ESMTP 12sm2095603fks.9
C: EHLO sender.example.com
S: 250-mx.example.com at your service,[172.31.135.47]
S: 250-SIZE 35651584
S: 250-8BITMIME
S: 250-AUTH LOGIN PLAIN OAUTHBEARER
S: 250-ENHANCEDSTATUSCODES
S: 250 PIPELINING
C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX
J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV
GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE=
S: 235 Authentication successful.
[connection continues...]
5.2. OAuth 1.0a Authorization with Channel Binding
This example shows channel binding in the context of an OAuth 1.0a
request using a keyed message digest. Note that line breaks are
inserted for readability.
S: * OK [CAPABILITY IMAP4rev1 AUTH=OAUTH10A-PLUS SASL-IR]
IMAP4rev1 Server Ready
C: t1 AUTHENTICATE OAUTH10A-PLUS cD10bHMtdW5pcXVlLGE9dXNlckBleGFtcGxlL
mNvbQFob3N0PXNlcnZlci5leGFtcGxlLmNvbQFwb3J0PTE0MwFhdXRoPU9BdXRoI
HJlYWxtPSJFeGFtcGxlIixvYXV0aF9jb25zdW1lcl9rZXk9IjlkamRqODJoNDhka
nM5ZDIiLG9hdXRoX3Rva2VuPSJra2s5ZDdkaDNrMzlzanY3IixvYXV0aF9zaWduY
XR1cmVfbWV0aG9kPSJITUFDLVNIQTEiLG9hdXRoX3RpbWVzdGFtcD0iMTM3MTMxM
jAxIixvYXV0aF9ub25jZT0iN2Q4ZjNlNGEiLG9hdXRoX3NpZ25hdHVyZT0iU1Nkd
ElHRWdiR2wwZEd4bElIUmxZU0J3YjNRdSIBcXM9Y2JkYXRhPXRscy11bmlxdWU6U
0c5M0lHSnBaeUJwY3lCaElGUk1VeUJtYVc1aGJDQnRaWE56WVdkbFB3bz0BAQ==
S: t1 OK SASL authentication succeeded
As required by IMAP [RFC3501], the payloads are base64-encoded. The
decoded initial client response (with %x01 represented as ^A and
lines wrapped for readability) is:
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p=tls-unique,a=user@example.com^A
host=server.example.com^A
port=143^A
auth=OAuth realm="Example",
oauth_consumer_key="9djdj82h48djs9d2",
oauth_token="kkk9d7dh3k39sjv7",
oauth_signature_method="HMAC-SHA1",
oauth_timestamp="137131201",
oauth_nonce="7d8f3e4a",
oauth_signature="SSdtIGEgbGl0dGxlIHRlYSBwb3Qu"^A
qs=cbdata=tls-unique:SG93IGJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=^A^A
In this example the signature base string with line breaks added for
readability would be:
POST&http%3A%2F%2Fserver.example.com:143%2F&cbdata=tls-unique:SG93I
GJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=%26oauth_consumer_key%3D9djd
j82h48djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_method%3DHM
AC-SHA1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39s
jv7
5.3. Failed Exchange
This example shows a failed exchange because of the empty
Authorization header, which is how a client can query for the needed
scope. Note that line breaks are inserted for readability.
S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR IMAP4rev1 Server
Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTHBEARER cD10bHMtdW5pcXVlLGE9dXNlckBleGFtcG
xlLmNvbQFob3N0PXNlcnZlci5leGFtcGxlLmNvbQFwb3J0PTE0MwFhdXRoP
QFjYmRhdGE9AQE=
S: + ewoic3RhdHVzIjoiNDAxIgoic2NvcGUiOiJleGFtcGxlX3Njb3BlIgp9
C: + AQ==
S: t1 NO SASL authentication failed
The decoded initial client response is:
n,a=user@example.com,^Ahost=server.example.com^A
port=143^Aauth=^A^A
The decoded server error response is:
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{
"status":"401",
"scope":"example_scope"
}
The client responds with the required dummy response.
5.4. Failed Channel Binding
This example shows a channel binding failure in an empty request.
The channel binding information is empty. Note that line breaks are
inserted for readability.
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH10A-PLUS SASL-IR IMAP4rev1 Server
Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH10A-PLUS cCxhPXVzZXJAZXhhbXBsZS5jb20BaG9z
dD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD0BY2JkYXRhPQEB
S: + ewoic3RhdHVzIjoiNDEyIiwKInNjb3BlIjoiZXhhbXBsZV9zY29wZSIKfQ==
C: + AQ==
S: t1 NO SASL authentication failed
The decoded initial client response is:
p=tls-unique,a=user@example.com,^Ahost=server.example.com^A
port=143^Aauth=^Acbdata=^A^A
The decoded server response is:
{
"status":"412",
"scope":"example_scope"
}
The client responds with the required dummy response.
5.5. SMTP Example of a Failed Negotiation
This example shows an authorization failure in an SMTP exchange.
Note that line breaks are inserted for readability, and that the SMTP
protocol terminates lines with CR and LF characters (ASCII values
0x0D and 0x0A), these are not displayed explicitly in the example.
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[connection begins]
S: 220 mx.example.com ESMTP 12sm2095603fks.9
C: EHLO sender.example.com
S: 250-mx.example.com at your service,[172.31.135.47]
S: 250-SIZE 35651584
S: 250-8BITMIME
S: 250-AUTH LOGIN PLAIN OAUTHBEARER
S: 250-ENHANCEDSTATUSCODES
S: 250 PIPELINING
C: AUTH OAUTHBEARER bixhPT1zb21ldXNlckBleGFtcGxlLmNvbQFhdXRoPUJlYXJlciB2
RjlkZnQ0cW1UYzJOdmIzUmxja0JoZEhSaGRtbHpkR0V1WTI5dENnPT0BAQ==
S: 334 eyJzdGF0dXMiOiI0MDEiLCJzY2hlbWVzIjoiYmVhcmVyIG1hYyIsInNjb3BlIjoia
HR0cHM6Ly9tYWlsLmdvb2dsZS5jb20vIn0K
C: AQ==
S: 535-5.7.1 Username and Password not accepted. Learn more at
S: 535 5.7.1 http://support.example.com/mail/oauth
[connection continues...]
The server returned an error message in the 334 SASL message, the
client responds with the required dummy response, and the server
finalizes the negotiation.
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6. Security Considerations
OAuth 1.0a and OAuth 2 allows for a variety of deployment scenarios,
and the security properties of these profiles vary. Application
developers therefore need to understand the needs of their
applications before selecting a specific SASL OAuth mechanism.
The channel binding in this mechanism has different properties based
on the Access Token Type used.
It is possible that SASL will be authenticating a connection and the
life of that connection may outlast the life of the access token used
to establish it. This is a common problem in application protocols
where connections are long-lived, and not a problem with this
mechanism per se. Servers MAY unilaterally disconnect clients in
accordance with the application protocol.
The OAuth access token (and related keying material) is not
equivalent to the user's long term password. As such, care has to be
taken when these OAuth credentials are used for actions like changing
passwords (as it is possible with some protocols, e.g., XMPP). The
server SHOULD ensure that actions taken in the authenticated channel
are appropriate to the strength of the presented credential.
Access tokens have a lifetime. Reducing the lifetime of an access
token provides security benefits, as described in
[I-D.ietf-oauth-v2-threatmodel], and OAuth 2.0 introduces refresh
tokens to obtain new access token on the fly. Additionally, a
previously obtained access token MAY be revoked or rendered invalid
at any time. The client MAY request a new access token for each
connection to a resource server, but it SHOULD cache and re-use
access credentials that appear to be valid.
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7. Internationalization Considerations
The identifer asserted by the OAuth authorization server about the
resource owner inside the access token may be displayed to a human.
For example, when SASL is used in the context of IMAP the resource
server may assert the resource owner's email address to the IMAP
server for usage in an email-based application. The identifier may
therefore contain internationalized characters and an application
needs to ensure that the mapping between the identifier provided by
OAuth is suitable for use with the application layer protocol SASL is
incorporated into.
At the time of writing the standardization of the assertion format
(in JSON format) is still ongoing, see
[I-D.ietf-oauth-json-web-token].
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8. IANA Considerations
8.1. SASL Registration
The IANA is requested to register the following SASL profile:
SASL mechanism profile: OAUTHBEARER
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: OAUTH10A
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: OAUTH10A-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
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8.2. GSS-API Registration
IANA is further requested to assign an OID for these GSS mechanisms
in the SMI numbers registry, with the prefix of
iso.org.dod.internet.security.mechanisms (1.3.6.1.5.5) and to
reference this specification in the registry.
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[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.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, November 2007.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[RFC5801] Josefsson, S. and N. Williams, "Using Generic Security
Service Application Program Interface (GSS-API) Mechanisms
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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.
[RFC6680] Williams, N., Johansson, L., Hartman, S., and S.
Josefsson, "Generic Security Service Application
Programming Interface (GSS-API) Naming Extensions",
RFC 6680, August 2012.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework",
RFC 6749, October 2012.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750, October 2012.
9.2. Informative References
[I-D.ietf-appsawg-webfinger]
Jones, P., Salgueiro, G., and J. Smarr, "WebFinger",
draft-ietf-appsawg-webfinger-07 (work in progress),
December 2012.
[I-D.ietf-oauth-json-web-token]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", draft-ietf-oauth-json-web-token-05 (work in
progress), November 2012.
[I-D.ietf-oauth-v2-http-mac]
Richer, J., Mills, W., and H. Tschofenig, "OAuth 2.0
Message Authentication Code (MAC) Tokens",
draft-ietf-oauth-v2-http-mac-02 (work in progress),
November 2012.
[I-D.ietf-oauth-v2-threatmodel]
Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0
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Threat Model and Security Considerations",
draft-ietf-oauth-v2-threatmodel-08 (work in progress),
October 2012.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
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Appendix A. Acknowlegements
The authors would like to thank the members of the Kitten working
group, and in addition and specifically: Simon Josefson, Torsten
Lodderstadt, Ryan Troll, Alexey Melnikov, and Nico Williams.
This document was produced under the chairmanship of Alexey Melnikov,
Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman. The area directors
included Stephen Farrell.
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Appendix B. Document History
[[ to be removed by RFC editor before publication as an RFC ]]
-09
o Incorporated review by Alexey and Hannes.
o Clarified the three OAuth SASL mechanisms.
o Updated references
o Extended acknowledgements
-08
o Fixed the channel binding examples for p=$cbtype
o More tuning of the authcid language and edited and renamed 3.2.1.
-07
o Struck the MUST langiage from authzid.
o
-06
o Removed the user field. Fixed the examples again.
o Added canonicalization language.
o
-05
o Fixed the GS2 header language again.
o Separated out different OAuth schemes into different SASL
mechanisms. Took out the scheme in the error return. Tuned up
the IANA registrations.
o Added the user field back into the SASL message.
o Fixed the examples (again).
o
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-04
o Changed user field to be carried in the gs2-header, and made gs2
header explicit in all cases.
o Converted MAC examples to OAuth 1.0a. Moved MAC to an informative
reference.
o Changed to sending an empty client response (single control-A) as
the second message of a failed sequence.
o Fixed channel binding prose to refer to the normative specs and
removed the hashing of large channel binding data, which brought
mroe problems than it solved.
o Added a SMTP examples for Bearer use case.
-03
o Added user field into examples and fixed egregious errors there as
well.
o Added text reminding developers that Authorization scheme names
are case insensitive.
-02
o Added the user data element back in.
o Minor editorial changes.
-01
o Ripping out discovery. Changed to refer to I-D.jones-appsawg-
webfinger instead of WF and SWD older drafts.
o Replacing HTTP as the message format and adjusted all examples.
-00
o Renamed draft into proper IETF naming format now that it's
adopted.
o Minor fixes.
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Authors' Addresses
William Mills
Yahoo! Inc.
Phone:
Email: wmills@yahoo-inc.com
Tim Showalter
Phone:
Email: 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
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