Internet DRAFT - draft-ietf-kitten-sasl-oauth
draft-ietf-kitten-sasl-oauth
KITTEN W. Mills
Internet-Draft Microsoft
Intended status: Standards Track T. Showalter
Expires: November 30, 2015
H. Tschofenig
ARM Ltd.
May 29, 2015
A set of SASL Mechanisms for OAuth
draft-ietf-kitten-sasl-oauth-23.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 November 30, 2015.
Copyright Notice
Copyright (c) 2015 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 . . . . . . . . . . . . . 6
3.1. Initial Client Response . . . . . . . . . . . . . . . . . 7
3.1.1. Reserved Key/Values . . . . . . . . . . . . . . . . . 8
3.2. Server's Response . . . . . . . . . . . . . . . . . . . . 8
3.2.1. OAuth Identifiers in the SASL Context . . . . . . . . 9
3.2.2. Server Response to Failed Authentication . . . . . . 9
3.2.3. Completing an Error Message Sequence . . . . . . . . 11
3.3. OAuth Access Token Types using Keyed Message Digests . . 11
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Successful Bearer Token Exchange . . . . . . . . . . . . 12
4.2. Successful OAuth 1.0a Token Exchange . . . . . . . . . . 13
4.3. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 14
4.4. SMTP Example of a Failed Negotiation . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 16
6. Internationalization Considerations . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Acknowlegements . . . . . . . . . . . . . . . . . . 20
Appendix B. Document History . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
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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]. 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 [RFC7230] 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 the Simple Mail Transfer Protocol (SMTP) [RFC5321].
This document gives examples of use in IMAP and SMTP.
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.
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----+
+--------+ +---------------+ |
| |--(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 -----| | |
| | | | |
+--------+ +---------------+ |
----+
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 mechanisms and allows old protocols to make
use of new authentication mechanisms. The framework also provides a
protocol for securing subsequent 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 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 the grant types defined in [RFC6749] or
[RFC5849] or using an extension grant type. The authorization
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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.
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,
authorization server endpoints, and client registration are outside
the scope of this specification. The client must discover the
authorization endpoints using a discovery mechanism such as OpenID
Connect Discovery [OpenID.Discovery] or Webfinger using host-meta
[RFC7033]. Once credentials are obtained the client proceeds to
steps (E) and (F) defined in this specification. Authorization
endpoints MAY require client registration and generic clients SHOULD
support the Dynamic Client Registration protocol
[I-D.ietf-oauth-dyn-reg].
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", "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] and SASL [RFC4422].
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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, as
specified in Section 4 of [RFC4648].
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: OAuth 2.0 bearer tokens, as described in [RFC6750].
RFC 6750 uses Transport Layer Security (TLS) [RFC5246] 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].
New extensions may be defined to add additional OAuth Access Token
Types. Such a new SASL OAuth mechanism can be added by registering
the new name(s) with IANA in the SASL Mechanisms registry and citing
this specification for the further definition.
SASL mechanisms using this document as their definition do not
provide a data security layer; that is, they cannot provide integrity
or confidentiality protection for application messages after the
initial authentication. If such protection is needed, TLS or some
similar solution should be used. Additionally, for the two
mechanisms specified in this document, TLS MUST be used for
OAUTHBEARER to protect the bearer token; for OAUTH10A the use of TLS
is RECOMMENDED.
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:
1. Client sends a valid and correct initial client response.
2. Server responds with a successful authentication.
In the case where authentication 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
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a SASL message and finalizing a SASL negotiation. The additional
client message in the error case deals with this problem. This
exchange is:
1. Client sends an invalid initial client response.
2. Server responds with an error message.
3. Client sends a dummy client response.
4. Server fails the authentication.
3.1. Initial Client Response
Client responses are a GS2 [RFC5801] header followed by zero or more
key/value pairs, or may be empty. The gs2-header is defined here for
compatibility with GS2 if a GS2 mechanism is formally defined, but
this document does not define one. The key/value pairs take the
place of the corresponding HTTP headers and values to convey the
information necessary 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
;;gs2-header = See RFC 5801
client_resp = (gs2-header kvsep *kvpair kvsep) / kvsep
The GS2 header MAY include the user name associated with the resource
being accessed, the "authzid". It is worth noting that application
protocols are allowed to require an authzid, as are specific server
implementations.
The client response consisting of only a single kvsep is used only
when authentication fails, and is only valid in that context. If
sent as the first message from the client the server MAY simply fail
the authentication without returning discovery information since
there is no user or server name indication.
The following keys and corresponding values are defined in the client
response:
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auth (REQUIRED): The payload that would be in the HTTP
Authorization header if this OAuth exchange was being carried
out over HTTP.
host: Contains the host name to which the client connected. In
an HTTP context this is the value of the HTTP Host header.
port: Contains the destination port that the client connected to,
represented as a decimal positive integer string without
leading zeros.
For OAuth token types such as OAuth 1.0a 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 are not accompanied by 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 include a keyed message digest of
the request 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 the empty
string ("").
qs (RESERVED): The HTTP query string, the default value is the
empty string ("").
3.2. Server's Response
The server validates the response according to 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.
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The server fully validates the client response before generating a
server response; this will necessarily include the validation steps
listed in the specification for the OAuth Access Token Type used.
However, additional validation steps may be needed, depending on the
particular application protocol making use of SASL. In particular,
values included as kvpairs in the client response (such as host and
port) which correspond to values known to the application server by
some other mechanism (such as an application protocol data unit or
pre-configured values) MUST be validated to match between the initial
client response and the the other source(s) of such information. As
a concrete example, when SASL is used over IMAP to an IMAP server for
a single domain the hostname can be available via configuration; this
hostname must be validated to match the value sent in the 'host'
kvpair.
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 authzid 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.
3.2.2. Server Response to Failed Authentication
For a failed authentication the server returns a JSON [RFC7159]
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 "OAuth Extensions Error Registry"
specified in the OAuth 2 core specification.
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scope (OPTIONAL): An OAuth scope which is valid to access the
service. This may be omitted which implies that unscoped
tokens are required. If a scope is specified then a single
scope is preferred. At the time this document was written
there are several implementations that do not properly support
space separated lists of scopes, so the use of a space
separated list of scopes is NOT RECOMMENDED.
openid-configuration (OPTIONAL): The URL for a document following
the OpenID Provider Configuration Information schema as
described in OpenID Connect Discovery (OIDCD)
[OpenID.Discovery] section 3 that is appropriate for the user.
As specified in OIDCD this will have the "https" URL scheme.
This document MUST have all OAuth related data elements
populated. The server MAY return different URLs for users in
different domains and the client SHOULD NOT cache a single
returned value and assume it applies for all users/domains that
the server suports. The returned discovery document SHOULD
have all data elements required by the OpenID Connect Discovery
specification populated. In addition, the discovery document
SHOULD contain the 'registration_endpoint' element to identify
the endpoint to be used with the Dynamic Client Registration
protocol [I-D.ietf-oauth-dyn-reg] to obtain the minimum number
of parameters necessary for the OAuth protocol exchange to
function. Another comparable discovery or client registration
mechanism MAY be used if available.
The use of the 'offline_access' scope, as defined in
[OpenID.Core] is RECOMMENDED to give clients the capability to
explicitly request a refresh token.
If the resource server provides a scope then the client MUST always
request scoped tokens from the token endpoint. If the resource
server does not return a scope the client SHOULD presume an unscoped
token is required to access the resource.
Since clients may interact with a number of application servers, such
as email servers and XMPP [RFC6120] servers, they need to have a way
to determine whether dynamic client registration has been performed
already and whether an already available refresh token can be re-used
to obtain an access token for the desired resource server. This
specification RECOMMENDs that a client uses the information in the
'iss' element defined in OpenID Connect Core [OpenID.Core] to make
this determination.
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3.2.3. Completing an Error Message Sequence
Section 3.6 of SASL [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 either 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 or send a SASL cancellation token as generally
defined in section 3.5 of SASL [RFC4422]. A specific example of a
cancellation token can be found in IMAP [RFC3501] section 6.2.2.
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.
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
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"^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.
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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
4. Examples
These examples illustrate exchanges between IMAP and SMTP clients and
servers. All IMAP examples use SASL-IR [RFC4959] and send payload in
the initial client response. The Bearer Token examples assume
encrypted transport; if the underlying connection is not already TLS
then STARTTLS MUST be used as TLS is required in the Bearer Token
specification.
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 in
IMAP. Note that line breaks are inserted for readability.
[Initial connection and TLS establishment...]
S: * OK IMAP4rev1 Server Ready
C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR
S: t0 OK Completed
C: t1 AUTH OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20sAWhvc3Q9c2Vy
dmVyLmV4YW1wbGUuY29tAXBvcnQ9MTQzAWF1dGg9QmVhcmVyIHZGOWRmd
DRxbVRjMk52YjNSbGNrQmhiSFJoZG1semRHRXVZMjl0Q2c9PQEB
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
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The same credential used in an SMTP exchange is shown below. Again
this example assumes that TLS is already established per the Bearer
Token specification requirements.
[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-STARTTLS
S: 250 PIPELINING
[Negotiate TLS...]
C: t1 AUTH OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20sAWhvc3Q9c2Vy
dmVyLmV4YW1wbGUuY29tAXBvcnQ9NTg3AWF1dGg9QmVhcmVyIHZGOWRmd
DRxbVRjMk52YjNSbGNrQmhiSFJoZG1semRHRXVZMjl0Q2c9PQEB
S: 235 Authentication successful.
[connection continues...]
The decoded initial client response is:
n,a=user@example.com,^Ahost=server.example.com^Aport=587^A
auth=Bearer vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg==^A^A
4.2. Successful OAuth 1.0a Token Exchange
This IMAP example shows a successful OAuth 1.0a token exchange. Note
that line breaks are inserted for readability. This example assumes
that TLS is already established. Signature computation is discussed
in Section 3.3.
S: * OK IMAP4rev1 Server Ready
C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER OAUTH10A SASL-IR
S: t0 OK Completed
C: t1 AUTH OAUTH10A bixhPXVzZXJAZXhhbXBsZS5jb20sAWhvc3Q9ZXhhb
XBsZS5jb20BcG9ydD0xNDMBYXV0aD1PQXV0aCByZWFsbT0iRXhhbXBsZSIsb2F1
dGhfY29uc3VtZXJfa2V5PSI5ZGpkajgyaDQ4ZGpzOWQyIixvYXV0aF90b2tlbj0
ia2trOWQ3ZGgzazM5c2p2NyIsb2F1dGhfc2lnbmF0dXJlX21ldGhvZD0iSE1BQy
1TSEExIixvYXV0aF90aW1lc3RhbXA9IjEzNzEzMTIwMSIsb2F1dGhfbm9uY2U9I
jdkOGYzZTRhIixvYXV0aF9zaWduYXR1cmU9IlRtOTBJR0VnY21WaGJDQnphV2R1
WVhSMWNtVSUzRCIBAQ==
S: t1 OK SASL authentication succeeded
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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:
n,a=user@example.com,^A
host=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^A
4.3. Failed Exchange
This IMAP 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: * OK IMAP4rev1 Server Ready
C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR
S: t0 OK Completed
C: t1 AUTH OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20sAW
hvc3Q9c2VydmVyLmV4YW1wbGUuY29tAXBvcnQ9MTQzAWF1dGg9AQE=
S: + eyJzdGF0dXMiOiJpbnZhbGlkX3Rva2VuIiwic2NvcGUiOiJleGFtcGxl
X3Njb3BlIiwib3BlbmlkLWNvbmZpZ3VyYXRpb24iOiJodHRwczovL2V4
YW1wbGUuY29tLy53ZWxsLWtub3duL29wZW5pZC1jb25maWcifQ==
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:
{
"status":"invalid_token",
"scope":"example_scope",
"openid-configuration":"https://example.com/.well-known/openid-config"
}
The client responds with the required dummy response, "AQ==" is the
base64 encoding of the ASCII value 0x01. The same exchange using the
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IMAP specific method of cancelling an AUTHENTICATE command sends "*"
and is shown below.
S: * OK IMAP4rev1 Server Ready
C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR IMAP4rev1
S: t0 OK Completed
C: t1 AUTH OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20sAW
hvc3Q9c2VydmVyLmV4YW1wbGUuY29tAXBvcnQ9MTQzAWF1dGg9AQE=
S: + eyJzdGF0dXMiOiJpbnZhbGlkX3Rva2VuIiwic2NvcGUiOiJleGFtcGxl
X3Njb3BlIiwib3BlbmlkLWNvbmZpZ3VyYXRpb24iOiJodHRwczovL2V4
YW1wbGUuY29tLy53ZWxsLWtub3duL29wZW5pZC1jb25maWd1cmF0aW9u
In0=
C: *
S: t1 NO SASL authentication failed
4.4. SMTP Example of a Failed Negotiation
This example shows an authorization failure in an SMTP exchange. TLS
negotiation is not shown but as noted above it is required for the
use of Bearer Tokens.
[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
[Negotiate TLS...]
C: AUTH OAUTHBEARER bix1c2VyPXNvbWV1c2VyQGV4YW1wbGUuY29tLAFhdXRoPUJlYXJl
ciB2RjlkZnQ0cW1UYzJOdmIzUmxja0JoZEhSaGRtbHpkR0V1WTI5dENnPT0BAQ==
S: 334 eyJzdGF0dXMiOiJpbnZhbGlkX3Rva2VuIiwic2NoZW1lcyI6ImJlYXJlciBtYWMiL
CJzY29wZSI6Imh0dHBzOi8vbWFpbC5leGFtcGxlLmNvbS8ifQ==
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 initial client response is:
n,user=someuser@example.com,^A
auth=Bearer vF9dft4qmTc2Nvb3RlckBhdHRhdmlzdGEuY29tCg==^A^A
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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.
{
"status":"invalid_token",
"schemes":"bearer mac",
"scope":"https://mail.example.com/"
}
5. Security Considerations
OAuth 1.0a and OAuth 2 allow 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 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 two 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
[RFC5849]. To compute the keyed message digest in the same way as
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.
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
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protocols, e.g., XMPP [RFC6120]). The resource server should
ensure that actions taken in the authenticated channel are
appropriate to the strength of the presented credential.
Lifetime of the application sessions.
It is possible that SASL will be used to authenticate 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 might 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 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 client 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 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
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7.1. SASL Registration
The IANA is requested to register the following entry in the SASL
Mechanisms registry:
SASL mechanism name: OAUTHBEARER
Security Considerations: See this document
Published Specification: See this document
For further information: Contact the authors of this document.
Intended usage: common
Owner/Change controller: the IESG
Note: None
The IANA is requested to register the following entry in the SASL
Mechanisms registry:
SASL mechanism name: OAUTH10A
Security Considerations: See this document
Published Specification: See this document
For further information: Contact the authors of this document.
Intended usage: common
Owner/Change controller: the IESG
Note: None
8. References
8.1. Normative References
[I-D.ietf-oauth-dyn-reg]
Richer, J., Jones, M., Bradley, J., Machulak, M., and P.
Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
draft-ietf-oauth-dyn-reg-27 (work in progress), March
2015.
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[OpenID.Core]
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0", February 2014.
[OpenID.Discovery]
Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
Connect Discovery 1.0", July 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[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.
[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.
[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.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014.
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-32 (work in
progress), December 2014.
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[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[RFC4959] Siemborski, R. and A. Gulbrandsen, "IMAP Extension for
Simple Authentication and Security Layer (SASL) Initial
Client Response", RFC 4959, September 2007.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
[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.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, June
2014.
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, Nico
Williams, Matt Miller, and Benjamin Kaduk.
This document was produced under the chairmanship of Alexey Melnikov,
Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman. The supervising area
director was Stephen Farrell.
Appendix B. Document History
[[ to be removed by RFC editor before publication as an RFC ]]
-23
o AD feedback from IESG review and comments.
o Fixed port number in SMTP examples.
o Minor editorial changes.
o Dyn-Reg draft becomes normative.
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o Added explicit TLS start indicator in all examples, removed text
that said we assume that.
-19
o Last call feedback agaiun.
o Clarified usage of TLS in examples and fixed them some more.
Adding reference to RFC4422 and cancellation token and an example
for that.
-18
o Last call feedback round #5. Fixed -17 change log.
o Corrected "issue" to "iss", other minor changes.
-17
o Last call feedback again (WGLC #4). eradicated comma splicing.
Removed extra server message in example 4.3.
o Added recommendations for discovery and dynamic client
registration support.
-16
o Last call feedback again. Primarily editorial changes. Corrected
examples.
-15
o Last call feedack on the GS2 stuff being ripped out completely.
o Removed the "user" parameter and put stuff back into the
gs2-header. Call out that the authzid goes in the gs2-header with
some prose about when it might be required. Very comparable to
-10.
o Added an OAuth 1.0A example explicitly.
-14
o Last call feedack on RFC citations needed, small editorial.
o Added the "user" parameter back, which was pulled when we started
down the GS2 path. Same language as -03.
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o Defined a stub GS2 header to make sure that when the GS2 bride is
defined for this that nothing will break when it actually starts
to get populated.
-13
o Changed affiliation.
-12
o Removed -PLUS components from the specification.
-11
o Removed GSS-API components from the specification.
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.
o
-06
o Removed the user field. Fixed the examples again.
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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
-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.
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-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.
Authors' Addresses
William Mills
Microsoft
Email: wimills@microsoft.com
Tim Showalter
Email: tjs@psaux.com
Hannes Tschofenig
ARM Ltd.
110 Fulbourn Rd
Cambridge CB1 9NJ
Great Britain
Email: Hannes.tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
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