One document matched: draft-ietf-kitten-sasl-oauth-12.xml
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<rfc ipr="trust200902" docName="draft-ietf-kitten-sasl-oauth-12.txt" category="std">
<front>
<title abbrev="SASL OAuth">A set of SASL 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_92105@yahoo.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 Solutions and 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="2013"/>
<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)
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
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.
</t>
</abstract>
</front>
<middle>
<!-- ******************************************************************** -->
<section title="Introduction">
<t>OAuth 1.0a <xref target="RFC5849"/> and OAuth 2.0 <xref target="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. </t>
<t>The core OAuth 2.0
specification <xref target="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 <xref
target="RFC6750"/> and the MAC Token specification <xref target="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 <xref target="RFC5849"/>.
</t>
<t>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) <xref target="RFC4422"/> 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>To illustrate the impact of integrating this specification into an OAuth-enabled application environment <xref target="overview"/> shows the abstract message flow of OAuth 2.0 <xref target="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.</t>
<t>
<figure anchor="overview" title="OAuth 2.0 Protocol Flow">
<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 -----| | |
| | | | |
+--------+ +---------------+ |
----+
]]></artwork>
</figure>
</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 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.</t>
<t>When OAuth is integrated into SASL 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>Again, steps (E) and (F) are not defined in <xref target="RFC6749"/>
(but are described in, for example, <xref target="RFC6750"/> for the OAuth Bearer Token instead) 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="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.
</t>
<t>OAuth 1.0 follows a similar model but uses a different terminology and
does not separate the resource server from the authorization server.</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:">OAuth 2.0 bearer tokens, as described in <xref target="RFC6750"/>. RFC 6750 uses
Transport Layer Security (TLS) to secure the protocol interaction between the client and the resource server.</t>
<t hangText="OAUTH10A:">OAuth 1.0a MAC tokens (using the HMAC-SHA1 keyed message digest), as described in Section
3.4.2 of <xref target="RFC5849"/>.
</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.
</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
]]></artwork>
</figure>
<!-- initial_client_resp = gs2-header kvsep client_resp
-->
</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. This is reserved for future use,
the client SHOUD NOT send it, and has the default value of "".
</t>
</list>
</t></list>
</t>
<t>
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. <!-- For 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 keyed message digest 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, 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 <xref target="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>
The "gs2-cb-flag" MUST be set to "n" because channel-binding <xref target="RFC5056"/>
data is not expected.
</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 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>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>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.</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 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.<!--, 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 Keyed Message Digests">
<t>
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.</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>
<!-- ******************************************************************** -->
<!--
<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 <xref target="RFC2743"/>,
</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>The setting of the security context flags depends on the selected mechanism:
<list style="symbols">
<t>OAUTHBEARER: The mutual_state flag (GSS_C_MUTUAL_FLAG) MUST be set to FALSE since the TLS
protocol execution happens outside the SASL/GSS-API method. Server-side authentication is
accomplished via the mandatory use of TLS at the application layer utilizing SASL. Without
TLS usage at the application layer protecting the by OAuth Bearer Token this SASL method is insecure.
</t>
<t>OAUTH10A: The mutual_state flag (GSS_C_MUTUAL_FLAG) MUST be set to FALSE since server
authentication is not provided by this SASL/GSS-API method. Since the TLS channel is managed
by the application outside of the GSS-API mechanism, the OAUTH10A 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>
</list>
Credential delegation is not supported by any of the SASL/GSS-API mechanisms with this specification.
Therefore, security contexts MUST have the deleg_state flag (GSS_C_DELEG_FLAG) set to FALSE.
</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 Section 4.1 of <xref target="RFC2743"/>).
These service names MUST be associated with the "entityID" claimed by
the RP.</t>
<t>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.</t>
<t>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 Section 4 of
<xref target="RFC2743"/>). The exported name token does, of course,
conform to Section 3.2 of <xref target="RFC2743"/>, 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 and the underlying TLS establishment is not shown either.</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="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="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. As shown in <xref target="overview"/> 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 <xref target="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 <xref target="RFC5849"/> provides guidance specific to OAuth 1.0.</t>
<t>This document specifies three SASL Mechanisms for OAuth and each comes with different security properties.
<list style="hanging">
<t hangText="OAUTHBEARER:">This mechanism borrows from OAuth 2.0 bearer tokens <xref target="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.</t>
<t hangText="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 <xref target="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.
</t>
</list>
</t>
<t>Additionally, the following aspects are worth pointing out:
<list style="hanging">
<t hangText="An access token is not equivalent to the user's long term password."><vspace blankLines="1"/>
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.</t>
<t hangText="Lifetime of the appliation sessions."><vspace blankLines="1"/>
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.</t>
<t hangText="Access tokens have a lifetime."><vspace blankLines="1"/>
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.</t>
</list>
</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 various claims in the access token (in JSON format) is still ongoing, see <xref target="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.</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>
</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.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.5849.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.5321.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3501.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.7033.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/bibxml/reference.RFC.6819.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, Jeffrey Hutzelman, and Nico Williams.
</t>
<t>
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.
</t>
</section>
<section title='Document History'>
<t>
[[ to be removed by RFC editor before publication as an RFC ]]
</t>
<t>
-12
</t>
<t>
<list style='symbols'>
<t>
Removed -PLUS components from the specification.
</t>
</list>
</t>
<t>
-11
</t>
<t>
<list style='symbols'>
<t>
Removed GSS-API components from the specification.
</t>
<t>
Updated security consideration section.
</t>
</list>
</t>
<t>
-10
</t>
<t>
<list style='symbols'>
<t>
Clarifications throughout the document in response to the feedback from Jeffrey Hutzelman.
</t>
</list>
</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>
| PAFTECH AB 2003-2026 | 2026-04-23 11:00:34 |