One document matched: draft-ietf-kitten-sasl-oauth-09.xml
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<!DOCTYPE rfc SYSTEM 'rfc2629.dtd'>
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<?rfc toc="yes"?>
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<rfc ipr="trust200902" docName="draft-ietf-kitten-sasl-oauth-09" category="std">
<front>
<title abbrev="SASL/GSS-API Mechanisms for OAuth">A set of SASL and GSS-API Mechanisms for OAuth</title>
<author fullname="William Mills" initials="W." surname="Mills">
<organization>Yahoo! Inc.</organization>
<address>
<postal>
<street/>
<city/>
<code/>
<region/>
<country/>
</postal>
<phone/>
<email>wmills@yahoo-inc.com </email>
</address>
</author>
<author fullname="Tim Showalter" initials="T." surname="Showalter">
<organization></organization>
<address>
<postal>
<street/>
<city/>
<code/>
<region/>
<country/>
</postal>
<phone/>
<email>tjs@psaux.com</email>
</address>
</author>
<author initials="H." surname="Tschofenig" fullname="Hannes Tschofenig">
<organization>Nokia Siemens Networks</organization>
<address>
<postal>
<street>Linnoitustie 6</street>
<city>Espoo</city>
<code>02600</code>
<country>Finland</country>
</postal>
<phone>+358 (50) 4871445</phone>
<email>Hannes.Tschofenig@gmx.net</email>
<uri>http://www.tschofenig.priv.at</uri>
</address>
</author>
<date year="2012"/>
<workgroup>KITTEN</workgroup>
<abstract>
<t>
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.
</t>
<t>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.
</t>
<t>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).
</t>
</abstract>
</front>
<middle>
<!-- ******************************************************************** -->
<section title="Introduction">
<t>OAuth <xref target="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 <xref target="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 <xref
target="RFC6750"/>, OAuth 2.0 MAC tokens <xref target="I-D.ietf-oauth-v2-http-mac"/>.
OAuth 1.0a <xref target="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.
</t>
<t><xref target="oauth-exchange"/> shows the abstract message flow as shown in Figure 1 of OAuth 2.0 <xref target="RFC6749"/>.</t>
<t>
<figure anchor="oauth-exchange" title="Abstract OAuth 2.0 Protocol Flow">
<artwork><![CDATA[
+--------+ +---------------+
| |--(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 ---| |
+--------+ +---------------+
]]></artwork>
</figure>
</t>
<t>This document takes
advantage of the OAuth protocol and its deployment base to provide a way to use
SASL <xref target="RFC4422"/> as well as the GSS-API <xref target="RFC2743"/> to gain
access to resources when using non-HTTP-based protocols, such as the Internet Message
Access Protocol (IMAP) <xref target="RFC3501"/> and SMTP <xref target="RFC5321"/>,
which is what this memo uses in the examples.</t>
<t>The Simple Authentication and Security Layer (SASL) is a framework
for providing authentication and data security services in
connection-oriented protocols via replaceable mechanisms. It
provides a structured interface between protocols and mechanisms.
The resulting framework allows new protocols to reuse existing
mechanisms and allows old protocols to make use of new mechanisms.
The framework also provides a protocol for securing subsequent
protocol exchanges within a data security layer.</t>
<t>
The Generic Security Service Application Program Interface (GSS-API)
<xref target="RFC2743"/> provides a framework for applications to support multiple
authentication mechanisms through a unified interface. </t>
<t>
This document
defines SASL mechanisms for OAuth, and it conforms to the new
bridge between SASL and the GSS-API called GS2 <xref target="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 <xref target="SASL-OAUTH"/>), and a second part
for those implementers that wish to implement the GSS-API portion (see
<xref target="GSSAPI-OAUTH"/>).
</t>
<t>When OAuth is integrated into SASL and the GSS-API the high-level steps are as follows:
<list style="empty">
<t> (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.</t>
<t> (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.</t>
<t> (C) The client requests an access token by authenticating with the
authorization server and presenting the authorization grant.</t>
<t> (D) The authorization server authenticates the client and validates
the authorization grant, and if valid issues an access token.</t>
<t> (E) The client requests the protected resource from the resource
server and authenticates by presenting the access token.</t>
<t> (F) The resource server validates the access token, and if valid,
indicates a successful authentication.</t>
</list>
</t>
<t>Steps (E) and (F) are not defined in <xref target="RFC6749"/> and are the
main functionality specified within this document.
Consequently, the message exchange shown in <xref target="overview"/> 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 <xref
target="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.
</t>
<t>
<figure anchor="overview" title="OAuth SASL Architecture">
<artwork><![CDATA[
----+
+--------+ +---------------+ |
| |--(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
+--------+ +---------------+ |
----+
]]></artwork>
</figure>
</t>
</section>
<!-- ******************************************************************** -->
<section anchor="terminology" title="Terminology">
<t>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
<xref target="RFC2119"/>.</t>
<t>The reader is assumed to be familiar with the terms used in the OAuth 2.0 specification <xref
target="RFC6749"/>.</t>
<t>In examples, "C:" and "S:" indicate lines sent by the client and server respectively. Line
breaks have been inserted for readability.</t>
<t>Note that the IMAP SASL specification requires base64 encoding, see Section 4 of <xref target="RFC4648"/>, not this memo.</t>
</section>
<!-- ******************************************************************** -->
<section anchor="SASL-OAUTH" title="OAuth SASL Mechanism Specifications">
<t>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:
<list><t>
<list style="hanging">
<t hangText="OAUTHBEARER:">Authorization using OAuth 2.0 bearer tokens as described in <xref target="RFC6750"/>.
</t>
<t hangText="OAUTH10A:">Authorization using OAuth 1.0a MAC tokens (using the HMAC-SHA1 keyed message digest) as described in Section 3.4.2 of <xref target="RFC5849"/>.
</t>
<t hangText="OAUTH10A-PLUS:">Adds channel binding <xref target="RFC5056"/> capability
to OAUTH10A for protection against man-in-the-middle attacks.
</t>
</list>
</t></list>
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.
</t>
<t>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:
<list style="symbols">
<t>Client sends a valid and correct initial client response.
</t>
<t>Server responds with a successful authentication.
</t>
</list>
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:
<list style="symbols">
<t>Client sends an invalid initial client response.</t>
<t>Server responds with an error message. </t>
<t>Client sends a dummy client response.</t>
<t>Server fails the authentication.</t>
</list>
</t>
<section title="Initial Client Response">
<t>Client responses are a key/value pair sequence. The initial client response
includes a gs2-header as defined in GS2 <xref target="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 <xref target="RFC5234"/> syntax is:
</t>
<t>
<figure>
<artwork>
<![CDATA[
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
]]></artwork>
</figure>
</t>
<t>The following key/value pairs are defined in the client response:
</t>
<t><list><t>
<list style="hanging">
<t hangText="auth (REQUIRED):">The payload of the HTTP Authorization header
for an equivalent HTTP OAuth authorization.</t>
<t hangText="host:">Contains the host name to which the client connected.</t>
<t hangText="port:">Contains the port number represented as a
decimal positive integer string without leading zeros
to which the client connected.</t>
<t hangText="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.
</t>
</list>
</t></list>
</t>
<t>
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.
</t>
<section title="Reserved Key/Values">
<t> 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:
<list><t>
<list style="hanging">
<t hangText="mthd (RESERVED):">HTTP method for use in signatures, the default value is "POST".
</t>
<t hangText="path (RESERVED):">HTTP path data, the default value is "/".
</t>
<t hangText="post (RESERVED):">HTTP post data, the default value is "".
</t>
</list>
</t></list>
</t>
</section>
<section title="Use of the gs2-header">
<t>The OAuth scheme related mechanisms are also GSS-API mechanisms, see
<xref target="GSSAPI-OAUTH" /> for further detail.
The gs2-header is used as follows:
<list style="symbols">
<t>The "gs2-nonstd-flag" MUST NOT be present.
</t>
<t>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.
</t>
</list>
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.
</t>
</section>
</section>
<section title="Server's Response">
<t>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.
</t>
<t>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.
</t>
<t> 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 <xref target="RFC4422"/>.
</t>
<section title="OAuth Identifiers in the SASL Context">
<t>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.</t>
<!--
<t>Some OAuth schemes can carry both an owner or resource identifier and a "proxy" identity,
for example an OAuth 1.0a <xref target="RFC5849"/>
mechanism where the consumer key (oauth_consumer_key) identifies the entity
using the token and the token itself identifies the owner or resouce.
-->
<t>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 <xref target="RFC2743"/> named type like GSS_C_NT_USER_NAME or
a comparable newly defined GSS-API name type or name attribute <xref target="RFC6680"/>.
</t>
</section>
<section title="Server Response to Failed Authentication">
<t>For a failed authentication the server returns a JSON <xref target="RFC4627"/>
formatted error result, and fails the authentication. The error result consists
of the following values:
<list><t>
<list style="hanging">
<t hangText="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.
</t>
<t hangText="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.
</t>
</list>
</t></list>
</t>
<t>If the resource server provides a scope then the client MUST always request scoped
tokens from the token endpoint.
<!--
The client MAY use a scope other than the one
provided by the resource server. Scopes other than those advertised by the
resource server are be defined by the resource owner and provided in service
documentation or discovery information (which is beyond the scope of this memo).
-->
If the resource server provides no scope to the client then the client SHOULD presume an empty scope (unscoped token) is needed.</t>
<t>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.
</t>
</section>
<section title="Completing an Error Message Sequence">
<t> Section 3.6 of <xref target="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.
</t>
</section>
</section>
<section title="OAuth Access Token Types using Digital Signatures and Keyed Message Digests">
<t>
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.</t>
<t>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. </t>
<t> 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:
</t>
<t><figure>
<artwork><![CDATA[
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
]]></artwork>
</figure>
</t>
<t>The signature base string would be constructed per the OAuth 1.0
specification <xref target="RFC5849" /> with the following things noted:
<list style="symbols">
<t>The method value is defaulted to POST.</t>
<t>The scheme defaults to be "http", and any port number other than 80 is included.</t>
<t>The path defaults to "/".</t>
<t>The query string defaults to "".</t>
</list>
In this example the signature base string with line breaks added for
readability would be:
</t>
<t><figure>
<artwork><![CDATA[
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
]]></artwork>
</figure>
</t>
</section>
<section title="Channel Binding">
<t>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.</t>
<t>The channel binding data is computed by the client based on it's choice of
preferred channel binding type. As specified in <xref target="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
<xref target="RFC5929"/>. </t>
</section>
</section>
<!-- ******************************************************************** -->
<section anchor="GSSAPI-OAUTH" title="GSS-API OAuth Mechanism Specification">
<t>Note: The normative references in this section are informational for SASL
implementers, but they are normative for GSS-API implementers.</t>
<t>A SASL OAuth mechanism is also a GSS-API mechanism and the messages
described in <xref target="SASL-OAUTH"/> are the same with the following
changes to the GS2 related elements:
<list style="numbers">
<t>the GS2 header on the client's first message is excluded when used as
a GSS-API mechanism.
</t>
<t>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,
</t>
</list>
</t>
<t>The GSS-API mechanism OIDs are:
<list style="symbols">
<t>OAUTHBEARER: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]</t>
<t>OAUTH10A: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]</t>
</list>
</t>
<t>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.
</t>
<t>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
<xref target="RFC6125"/>. For example, when SASL OAuth is run over IMAP
then the IMAP profile of RFC 6125 is used.</t>
<t>OAuth mechanisms do not support per-message tokens or
GSS_Pseudo_random.</t>
<t>OAuth supports a standard generic name syntax for acceptors, such as
GSS_C_NT_HOSTBASED_SERVICE (see <xref target="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;
applications SHOULD use generic GSS-API name types, such as
GSS_C_NT_USER_NAME and GSS_C_NT_HOSTBASED_SERVICE (see <xref target="RFC2743"/>,
Section 4). The exported name token does, of course, conform to
<xref target="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.
</t>
</section>
<!-- ******************************************************************** -->
<section title="Examples">
<t>These examples illustrate exchanges between an IMAP and SMTP clients and servers.</t>
<t>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".
</t>
<section title="Successful Bearer Token Exchange">
<t>This example shows a successful OAuth 2.0 bearer token exchange. Note that line
breaks are inserted for readability.</t>
<t>
<figure>
<artwork><![CDATA[
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
]]></artwork>
</figure>
</t>
<t>As required by IMAP <xref target="RFC3501"/>, the payloads are base64-encoded. The
decoded initial client response (with %x01 represented as ^A and long lines
wrapped for readability) is:
</t>
<t><figure>
<artwork><![CDATA[
n,a=user@example.com^Ahost=server.example.com^Aport=143^A
auth=Bearer vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg==^A^A
]]></artwork>
</figure>
</t>
<t>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.</t>
<t>
<figure>
<artwork><![CDATA[
[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...]
]]></artwork>
</figure>
</t>
</section>
<!-- ******************************************************************** -->
<section title="OAuth 1.0a Authorization with Channel Binding">
<t>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.</t>
<t>
<figure>
<artwork><![CDATA[
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
]]></artwork>
</figure>
</t>
<t>As required by IMAP <xref target="RFC3501"/>, the payloads are
base64-encoded. The
decoded initial client response (with %x01 represented as ^A and lines
wrapped for readability) is: </t>
<t>
<figure>
<artwork><![CDATA[
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
]]></artwork>
</figure>
In this example the signature base string with line breaks added for
readability would be:
</t>
<t><figure>
<artwork><![CDATA[
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
]]></artwork>
</figure>
</t>
</section>
<!-- ******************************************************************** -->
<section title="Failed Exchange">
<t>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.</t>
<t>
<figure>
<artwork><![CDATA[
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
]]></artwork>
</figure>
</t>
<t> The decoded initial client response is: </t>
<t>
<figure>
<artwork><![CDATA[
n,a=user@example.com,^Ahost=server.example.com^A
port=143^Aauth=^A^A
]]></artwork>
</figure>
</t>
<t> The decoded server error response is: </t>
<t>
<figure>
<artwork><![CDATA[
{
"status":"401",
"scope":"example_scope"
}
]]></artwork>
</figure>
</t>
<t>The client responds with the required dummy response.
</t>
</section>
<!-- ******************************************************************** -->
<section title="Failed Channel Binding">
<t>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.</t>
<t>
<figure>
<artwork><![CDATA[
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
]]></artwork>
</figure>
</t>
<t> The decoded initial client response is: </t>
<t>
<figure>
<artwork><![CDATA[
p=tls-unique,a=user@example.com,^Ahost=server.example.com^A
port=143^Aauth=^Acbdata=^A^A
]]></artwork>
</figure>
</t>
<t> The decoded server response is: </t>
<t>
<figure>
<artwork><![CDATA[
{
"status":"412",
"scope":"example_scope"
}
]]></artwork>
</figure>
</t>
<t>The client responds with the required dummy response.
</t>
</section>
<!-- ******************************************************************** -->
<section title="SMTP Example of a Failed Negotiation">
<t>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.</t>
<t>
<figure>
<artwork><![CDATA[
[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...]
]]></artwork>
</figure>
</t>
<t>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.
</t>
</section>
<!-- ******************************************************************** -->
</section>
<!-- ******************************************************************** -->
<section title="Security Considerations">
<t>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.</t>
<t>The channel binding in this mechanism has different properties based
on the Access Token Type used.</t>
<t>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.</t>
<t>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.</t>
<t>Access tokens have a lifetime. Reducing the lifetime of an access
token provides security benefits, as described in <xref target="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.</t>
</section>
<!-- ******************************************************************** -->
<section title="Internationalization Considerations">
<t>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.</t>
<t>At the time of writing the standardization of the assertion format (in JSON format) is still ongoing, see <xref target="I-D.ietf-oauth-json-web-token"/>.</t>
</section>
<!-- ******************************************************************** -->
<section title="IANA Considerations">
<section title="SASL Registration">
<t> The IANA is requested to register the following SASL profile: <list style="empty">
<t>SASL mechanism profile: OAUTHBEARER</t>
<t>Security Considerations: See this document</t>
<t>Published Specification: See this document</t>
<t>For further information: Contact the authors of this document.</t>
<t>Owner/Change controller: the IETF</t>
<t>Note: None</t>
</list>
</t>
<t> The IANA is requested to register the following SASL profile: <list style="empty">
<t>SASL mechanism profile: OAUTH10A</t>
<t>Security Considerations: See this document</t>
<t>Published Specification: See this document</t>
<t>For further information: Contact the authors of this document.</t>
<t>Owner/Change controller: the IETF</t>
<t>Note: None</t>
</list>
</t>
<t> The IANA is requested to register the following SASL profile: <list style="empty">
<t>SASL mechanism profile: OAUTH10A-PLUS</t>
<t>Security Considerations: See this document</t>
<t>Published Specification: See this document</t>
<t>For further information: Contact the authors of this document.</t>
<t>Owner/Change controller: the IETF</t>
<t>Note: None</t>
</list>
</t>
</section>
<section title="GSS-API Registration">
<t>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.</t>
</section>
</section>
<!-- ******************************************************************** -->
<!-- ******************************************************************** -->
</middle>
<back>
<references title="Normative References">
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2473.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2616.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2617.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3174.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4422.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4627.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5056.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5246.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5234.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5321.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5849.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5929.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5988.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2743.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5801.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.6125.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.6680.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4648.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.6749.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.6750.xml' ?>
</references>
<references title="Informative References">
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3501.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-appsawg-webfinger.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-oauth-json-web-token.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-oauth-v2-http-mac.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-oauth-v2-threatmodel.xml' ?>
</references>
<section title='Acknowlegements'>
<t>
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.
</t>
<t>
This document was produced under the chairmanship of Alexey Melnikov, Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman.
The area directors included
Stephen Farrell.
</t>
</section>
<section title='Document History'>
<t>
[[ to be removed by RFC editor before publication as an RFC ]]
</t>
<t>
-09
</t>
<t>
<list style='symbols'>
<t>
Incorporated review by Alexey and Hannes.
</t>
<t>
Clarified the three OAuth SASL mechanisms.
</t>
<t>Updated references</t>
<t>Extended acknowledgements</t>
</list>
</t>
<t>
-08
</t>
<t>
<list style='symbols'>
<t>
Fixed the channel binding examples for p=$cbtype
</t>
<t>
More tuning of the authcid language and edited and renamed 3.2.1.
</t>
</list>
</t>
<t>
-07
</t>
<t>
<list style='symbols'>
<t>
Struck the MUST langiage from authzid.
</t>
<t>
</t>
</list>
</t>
<t>
-06
</t>
<t>
<list style='symbols'>
<t>
Removed the user field. Fixed the examples again.
</t>
<t>Added canonicalization language.
</t>
<t>
</t>
</list>
</t>
<t>
-05
</t>
<t>
<list style='symbols'>
<t>
Fixed the GS2 header language again.
</t>
<t>
Separated out different OAuth schemes into different SASL mechanisms. Took out the
scheme in the error return. Tuned up the IANA registrations.
</t>
<t>
Added the user field back into the SASL message.
</t>
<t>
Fixed the examples (again).
</t>
<t>
</t>
</list>
</t>
<t>
-04
</t>
<t>
<list style='symbols'>
<t>
Changed user field to be carried in the gs2-header, and made gs2 header explicit in all cases.
</t>
<t>
Converted MAC examples to OAuth 1.0a. Moved MAC to an informative reference.
</t>
<t>
Changed to sending an empty client response (single control-A) as the second message of a failed sequence.
</t>
<t>
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.
</t>
<t>
Added a SMTP examples for Bearer use case.
</t>
</list>
</t>
<t>
-03
</t>
<t>
<list style='symbols'>
<t>
Added user field into examples and fixed egregious errors there as well.
</t>
<t>
Added text reminding developers that Authorization scheme names are case insensitive.
</t>
</list>
</t>
<t>
-02
</t>
<t>
<list style='symbols'>
<t>
Added the user data element back in.
</t>
<t>
Minor editorial changes.
</t>
</list>
</t>
<t>
-01
</t>
<t>
<list style='symbols'>
<t>
Ripping out discovery. Changed to refer to I-D.jones-appsawg-webfinger instead
of WF and SWD older drafts.
</t>
<t>
Replacing HTTP as the message format and adjusted all examples.
</t>
</list>
</t>
<t>
-00
</t>
<t>
<list style='symbols'>
<t>
Renamed draft into proper IETF naming format now that it's adopted.
</t>
<t>
Minor fixes.
</t>
</list>
</t>
</section>
</back>
</rfc>
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