A set of SASL Mechanisms for OAuth
draft-ietf-kitten-sasl-oauth-11
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (kitten WG) | |
|---|---|---|---|
| Authors | William Mills , Tim Showalter , Hannes Tschofenig | ||
| Last updated | 2013-10-17 | ||
| Replaces | draft-mills-kitten-sasl-oauth | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-kitten-sasl-oauth-11
KITTEN W. Mills
Internet-Draft Yahoo! Inc.
Intended status: Standards Track T. Showalter
Expires: April 20, 2014
H. Tschofenig
Nokia Solutions and Networks
October 17, 2013
A set of SASL Mechanisms for OAuth
draft-ietf-kitten-sasl-oauth-11.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 credentials
obtained via OAuth over the Simple Authentication and Security Layer
(SASL) 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 shared
secret with higher entropy, i.e., the token. Tokens typically
provide limited access rights and can be managed and revoked
separately from the user's long-term 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 April 20, 2014.
Copyright Notice
Copyright (c) 2013 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. OAuth SASL Mechanism Specifications . . . . . . . . . . . . . 5
3.1. Initial Client Response . . . . . . . . . . . . . . . . . 7
3.1.1. Reserved Key/Values . . . . . . . . . . . . . . . . . 7
3.2. Server's Response . . . . . . . . . . . . . . . . . . . . 8
3.2.1. OAuth Identifiers in the SASL Context . . . . . . . . 8
3.2.2. Server Response to Failed Authentication . . . . . . 9
3.2.3. Completing an Error Message Sequence . . . . . . . . 9
3.3. OAuth Access Token Types using Keyed Message Digests . . 9
3.4. Channel Binding . . . . . . . . . . . . . . . . . . . . . 10
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Successful Bearer Token Exchange . . . . . . . . . . . . 11
4.2. OAuth 1.0a Authorization with Channel Binding . . . . . . 12
4.3. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 13
4.4. Failed Channel Binding . . . . . . . . . . . . . . . . . 14
4.5. SMTP Example of a Failed Negotiation . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15
6. Internationalization Considerations . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 17
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Acknowlegements . . . . . . . . . . . . . . . . . . 19
Appendix B. Document History . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
OAuth 1.0a [RFC5849] and OAuth 2.0 [RFC6749] are protocol frameworks
that enable 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] specifies the interaction
between the OAuth client and the authorization server; it does not
define the interaction between the OAuth client and the resource
server for the access to a protected resource using an Access Token.
Instead, the OAuth client to resource server interaction is described
in separate specifications, such as the bearer token specification
[RFC6750] and the MAC Token specification
[I-D.ietf-oauth-v2-http-mac]. OAuth 1.0a included the protocol
specification for the communication between the OAuth client and the
resource server in [RFC5849].
The main use cases for OAuth 2.0 and OAuth 1.0a have so far focused
on an HTTP-based environment only. This document integrates OAuth
1.0a and OAuth 2.0 into non-HTTP-based applications using the
integration into SASL. Hence, this document takes advantage of the
OAuth protocol and its deployment base to provide a way to use the
Simple Authentication and Security Layer (SASL) [RFC4422] 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.
To illustrate the impact of integrating this specification into an
OAuth-enabled application environment Figure 1 shows the abstract
message flow of OAuth 2.0 [RFC6749]. As indicated in the figure,
this document impacts the exchange of messages (E) and (F) since SASL
is used for interaction between the client and the resource server
instead of HTTP.
----+
+--------+ +---------------+ |
| |--(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) +---------------+ |
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| | ----+
| | ----+
| | +---------------+ |
| | | | |OAuth
| |--(E)------ Access Token -------->| Resource | |over
| | | Server | |SASL
| |<-(F)---- Protected Resource -----| | |
| | | | |
+--------+ +---------------+ |
----+
Figure 1: OAuth 2.0 Protocol Flow
The Simple Authentication and Security Layer (SASL) is a framework
for providing authentication and data security services in
connection-oriented protocols via replaceable authentication
mechanisms. It provides a structured interface between protocols and
mechanisms. The resulting framework allows new protocols to reuse
existing authentication protocols and allows old protocols to make
use of new authentication mechanisms. The framework also provides a
protocol for securing subsequent protocol exchanges within a data
security layer.
When OAuth is integrated into SASL 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.
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(F) The resource server validates the access token, and if valid,
indicates a successful authentication.
Again, steps (E) and (F) are not defined in [RFC6749] (but are
described in, for example, [RFC6750] for the OAuth Bearer Token
instead) and are the main functionality specified within this
document. Consequently, the message exchange shown in Figure 1 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 [RFC7033].
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.
OAuth 1.0 follows a similar model but uses a different terminology
and does not separate the resource server from the authorization
server.
2. Terminology
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.
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:
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OAUTHBEARER: OAuth 2.0 bearer tokens, as described in [RFC6750].
RFC 6750 uses Transport Layer Security (TLS) to secure the
protocol interaction between the client and the resource
server.
OAUTH10A: 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.
OAUTH10A-PLUS mandates the usage of Transport Layer Security
(TLS).
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.
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.
o Server fails the authentication.
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3.1. Initial Client Response
Client responses are a key/value pair sequence. 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
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 token types that use keyed message digests the client MUST
send host and port number key/values, and the server MUST fail an
authorization request requiring keyed message digests that do not
have host and port values. In OAuth 1.0a for example, the so-called
"signature base string calculation" includes the reconstructed HTTP
URL.
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 keyed message digest
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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, the default value is "POST".
path (RESERVED): HTTP path data, the default value is "/".
post (RESERVED): HTTP post data, the default value is "".
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
keyed message digest of the request parameters then the client must
provide a client response that satisfies the data requirements for
the scheme in use.
In a "-PLUS" mechanism the server examines the channel binding data,
extracts the channel binding unique prefix, and extracts the raw
channel biding data based on the channel binding type used. It then
computes it's own copy of the channel binding payload and compares
that to the payload sent by the client in the cbdata key/value.
Those two must be equal for channel binding to succeed.
The server responds to a successfully verified client message by
completing the SASL negotiation. The authenticated identity reported
by the SASL mechanism is the identity securely established for the
client with the OAuth credential. The application, not the SASL
mechanism, based on local access policy determines whether the
identity reported by the mechanism is allowed access to the requested
resource. Note that the semantics of the authz-id is specified by
the SASL framework [RFC4422].
3.2.1. OAuth Identifiers in the SASL Context
In the OAuth framework the client may be authenticated by the
authorization server and the resource owner is authenticated to the
authorization server. OAuth access tokens may contain information
about the authentication of the resource owner and about the client
and may therefore make this information accessible to the resource
server.
If both identifiers are needed by an application the developer will
need to provide a way to communicate that from the SASL mechanism
back to the application.
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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
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 Keyed Message Digests
OAuth Access Token Types may use keyed message digests and the client
and the resource server may 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.
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The default HTTP path is "/" and the default post body is empty.
These atoms are defined as extension points so that no changes are
needed if there is a revision of SASL which supports more specific
resource authorization, e.g., IMAP access to a specific folder or FTP
access limited to a specific directory.
Using the example in the OAuth 1.0a specification as a starting
point, on an IMAP server running on port 143 and given the OAuth 1.0a
style authorization request (with %x01 shown as ^A and line breaks
added for readability) below:
n,a=user@example.com^A
host=example.com^A
user=user@example.com^A
port=143^A
auth=OAuth realm="Example",
oauth_consumer_key="9djdj82h48djs9d2",
oauth_token="kkk9d7dh3k39sjv7",
oauth_signature_method="HMAC-SHA1",
oauth_timestamp="137131201",
oauth_nonce="7d8f3e4a",
oauth_signature="Tm90IGEgcmVhbCBzaWduYXR1cmU%3D"^A^A
The signature base string would be constructed per the OAuth 1.0
specification [RFC5849] with the following things noted:
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
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"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
OAuth 2.0 Bearer Token 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].
4. 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".
4.1. Successful Bearer Token Exchange
This example shows a successful OAuth 2.0 bearer token exchange.
Note that line breaks are inserted for readability and the underlying
TLS establishment is not shown either.
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:
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n,a=user@example.com^Ahost=server.example.com^Aport=143^A
auth=Bearer vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg==^A^A
The same credential used in an SMTP exchange is shown below. Note
that line breaks are inserted for readability, and that the SMTP
protocol terminates lines with CR and LF characters (ASCII values
0x0D and 0x0A), these are not displayed explicitly in the example.
[connection begins]
S: 220 mx.example.com ESMTP 12sm2095603fks.9
C: EHLO sender.example.com
S: 250-mx.example.com at your service,[172.31.135.47]
S: 250-SIZE 35651584
S: 250-8BITMIME
S: 250-AUTH LOGIN PLAIN OAUTHBEARER
S: 250-ENHANCEDSTATUSCODES
S: 250 PIPELINING
C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX
J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV
GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE=
S: 235 Authentication successful.
[connection continues...]
4.2. 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
4.3. 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.
4.4. 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.
4.5. 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.
5. Security Considerations
OAuth 1.0a and OAuth 2 allows for a variety of deployment scenarios,
and the security properties of these profiles vary. As shown in
Figure 1 this specification is aimed to be integrated into a larger
OAuth deployment. Application developers therefore need to
understand the needs of their security requirements based on a threat
assessment before selecting a specific SASL OAuth mechanism. For
OAuth 2.0 a detailed security document [RFC6819] provides guidance to
select those OAuth 2.0 components that help to mitigate threats for a
given deployment. For OAuth 1.0a Section 4 of RFC 5849 [RFC5849]
provides guidance specific to OAuth 1.0.
This document specifies three SASL Mechanisms for OAuth and each
comes with different security properties.
OAUTHBEARER: This mechanism borrows from OAuth 2.0 bearer tokens
[RFC6750]. It relies on the application using TLS to protect the
OAuth 2.0 Bearer Token exchange; without TLS usage at the
application layer this method is completely insecure.
Consequently, TLS MUST be provided by the application when
choosing this authentication mechanism.
OAUTH10A: This mechanism re-uses OAuth 1.0a MAC tokens (using the
HMAC-SHA1 keyed message digest), as described in Section 3.4.2 of
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[RFC5849]. To compute the keyed message digest in the same way
was in RFC 5839 this specification conveys additional parameters
between the client and the server. This SASL mechanism only
supports client authentication. If server-side authentication is
desireable then it must be provided by the application underneath
the SASL layer. The use of TLS is strongly RECOMMENDED.
OAUTH10A-PLUS: This mechanism adds the channel binding [RFC5056]
capability to OAUTH10A for protection against man-in-the-middle
attacks. OAUTH10A-PLUS mandates the usage of Transport Layer
Security (TLS) at the application layer.
Additionally, the following aspects are worth pointing out:
An access token is not equivalent to the user's long term password.
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 resource server should ensure that
actions taken in the authenticated channel are appropriate to the
strength of the presented credential.
Lifetime of the appliation sessions.
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. Resource servers may
unilaterally disconnect clients in accordance with the application
protocol.
Access tokens have a lifetime.
Reducing the lifetime of an access token provides security
benefits and OAuth 2.0 introduces refresh tokens to obtain new
access token on the fly without any need for a human interaction.
Additionally, a previously obtained access token may be revoked or
rendered invalid at any time by the authorization server. The
client may request a new access token for each connection to a
resource server, but it should cache and re-use valid credentials.
6. 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
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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 various claims in
the access token (in JSON format) is still ongoing, see
[I-D.ietf-oauth-json-web-token]. Once completed it will provide a
standardized format for exchanging identity information between the
authorization server and the resource server.
7. IANA Considerations
7.1. 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
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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
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[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.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
6749, October 2012.
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Internet-Draft SASL OAuth October 2013
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750, October 2012.
8.2. Informative References
[I-D.ietf-oauth-json-web-token]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", draft-ietf-oauth-json-web-token-12 (work in
progress), October 2013.
[I-D.ietf-oauth-v2-http-mac]
Richer, J., Mills, W., Tschofenig, H., and P. Hunt, "OAuth
2.0 Message Authentication Code (MAC) Tokens", draft-ietf-
oauth-v2-http-mac-04 (work in progress), July 2013.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[RFC6819] Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0
Threat Model and Security Considerations", RFC 6819,
January 2013.
[RFC7033] Jones, P., Salgueiro, G., Jones, M., and J. Smarr,
"WebFinger", RFC 7033, September 2013.
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, Jeffrey Hutzelman, and Nico
Williams.
This document was produced under the chairmanship of Alexey Melnikov,
Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman. The supervising area
directors was Stephen Farrell.
Appendix B. Document History
[[ to be removed by RFC editor before publication as an RFC ]]
-12
o Removed GSS-API components from the specification.
-11
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o Updated security consideration section.
-10
o Clarifications throughout the document in response to the feedback
from Jeffrey Hutzelman.
-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.
-06
o Removed the user field. Fixed the examples again.
o Added canonicalization language.
-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).
-04
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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.
Email: wmills@yahoo-inc.com
Tim Showalter
Email: tjs@psaux.com
Hannes Tschofenig
Nokia Solutions and 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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