One document matched: draft-ietf-kitten-sasl-oauth-00.xml
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<?rfc toc="yes"?>
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<rfc ipr="trust200902" docName="draft-ietf-kitten-sasl-oauth-00.txt" category="std">
<front>
<title abbrev="A SASL/GSS-API Mechanism for OAuth">A SASL and GSS-API Mechanism 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>Yahoo! Inc.</organization>
<address>
<postal>
<street/>
<city/>
<code/>
<region/>
<country/>
</postal>
<phone/>
<email>timshow@yahoo-inc.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="2011"/>
<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 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, and additionally defines
authorization and token issuing endpoint discovery. 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="I-D.ietf-oauth-v2"/> 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
specification <xref target="I-D.ietf-oauth-v2"/> 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 two separate specifications, namely <xref
target="I-D.ietf-oauth-v2-bearer"/>, and <xref
target="I-D.ietf-oauth-v2-http-mac"/>, whereby the focus is on an HTTP-based environment only.
</t>
<t><xref target="oauth-exchange"/> shows the abstract message flow as shown in Figure 1 of <xref target="I-D.ietf-oauth-v2"/>.</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"/>, 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 a SASL mechanism for OAuth, but it conforms to the new
bridge between SASL and the GSS-API called GS2 <xref target="RFC5801"/>. This means
that this document defines both a SASL mechanism and a GSS-API
mechanism. Implementers may be interested in
either the SASL, the GSS-API, or even both mechanisms. To
faciliate 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,
serves the request.</t>
</list>
</t>
<t>Steps (E) and (F) are not defined in <xref
target="I-D.ietf-oauth-v2"/> and are the main functionality specified within this document.
Additionally, an optional discovery exchange is defined. Consequently, the message exchange shown in <xref target="overview"/> is the result of this specification.
(1) and (2) denote the optional discovery exchange steps that may happen before the OAuth 2.0 protocol
exchange messages in steps (A)-(D) are executed. Steps (E) and (F) also 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) +---------------+ |
| | ----+
| |
| | ----+
| | (Optional discovery) +---------------+ |
| |--(1)------- User Name --------->| | |
| Client | | | |
| |<-(2)------ Authentication -------| | |
| | endpoint information | Resource | |OAuth
| | | Server | |over
| |--(E)------ Access Token -------->| | |SASL/
| | | | |GSS-
| |<-(F)---- Protected Resource -----| | |API
+--------+ +---------------+ |
----+
]]></artwork>
</figure>
</t>
<t>
<list style="empty">
<t>Note: The discovery procedure in OAuth is still work in progress. Hence, the discovery
components described in this document should be considered incomplete and a tentative
proposal. In general, there is a trade off between a generic, externally available
defined discovery mechanisms (such as Webfinger using host-meta <xref
target="I-D.hammer-hostmeta"/>, or <xref target="I-D.jones-simple-web-discovery"/>) and configuration information exchanged in-band between
the SASL communication endpoints. </t>
</list>
</t>
<t>It is worthwhile to note that this specification is also compatible with OAuth 1.0a <xref
target="RFC5849"/>.</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="I-D.ietf-oauth-v2"/>.</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 message, not this memo.</t>
</section>
<!-- ******************************************************************** -->
<section anchor="SASL-OAUTH" title="OAuth SASL Mechanism Specification">
<t>SASL is used as a generalized authentication method in a variety of application layer protocols. This
document defines two SASL mechanisms for usage with OAuth: "OAUTH" and "OAUTH-PLUS". The "OAUTH" SASL
mechanism provides bearer token alike semantic for SASL while "OAUTH-PLUS" provides a semantic similar to
OAuth MAC authentication by utilizing a channel binding mechanism <xref target="RFC5056"/>.</t>
<section title="Channel Binding">
<t>If the specification for the underlying
authorization scheme requires a security layer, such as TLS <xref target="RFC5246"/>, the server
SHOULD only offer a mechanism where channel binding can be enabled.</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 if the raw channel binding data is less than 500 bytes. If the raw channel binding data is 500 bytes or
larger then a SHA-1 <xref target="RFC3174"/> hash of
the raw channel binding data is computed.</t>
<t>If the client is using tls-unique for a channel binding then the raw channel
binding data equals the first TLS finished message. This is under the 500 byte
limit, so the channel binding payload sent to the server would be the base64
encoded first TLS finished message.</t>
<t>In the case where the client has chosen tls-endpoint, the raw channel binding
data is the certificate of the server the client connected to, which will
frequently be 500 bytes or more. If it is then the channel binding payload
is the base64 encoded SHA-1 hash of the server certificate.</t>
</section>
<section title="Initial Client Response">
<t>The SASL client response is formatted as an HTTP <xref target="RFC2616"/> request. The HTTP request is limited in
that the path MUST be "/". In the OAUTH mechanism no query string is allowed. The following header lines are
defined in the client response:
<list><t>
<list style="hanging">
<t hangText="User (OPTIONAL):">Contains the user identifier being authenticated, and is
provided to allow correct discovery information to be returned.</t>
<t hangText="Host (REQUIRED):">Contains the host name to which the client connected.</t>
<t hangText="Authorization (REQUIRED):">An HTTP Authorization header.</t>
</list>
</t></list>
</t>
<t> The user name is provided by the client to allow the discovery information to be
customized for the user, a given server could allow multiple authenticators and it needs to
return the correct one. For instance, a large ISP could provide mail service for
several domains who manage their own user information. For instance, users at foo-example.com
could be authenticated by an OAuth service at https://oauth.foo-example.com/, and users at
bar-example.com could be authenticated by https://oauth.bar-example.com, but both could be served
by a hypothetical IMAP server running at a third domain, imap.example.net. </t>
<section title="Query String in OAUTH-PLUS">
<t> In the OAUTH-PLUS mechanism the channel binding information is carried in
the query string. OAUTH-PLUS defines following query parameter(s):
<list><t>
<list style="hanging">
<t hangText="cbdata (REQUIRED):">Contains the
base64 encoded channel binding data, properly
escaped as an HTML query parameter value.</t>
</list>
</t></list>
</t>
</section>
</section>
<section title="Server's Response">
<t>The server validates the response per the specification for the authorization
scheme used. If the authorization scheme used includes signing of the request
parameters the client must provide a complete HTTP style request that satisfies
the data requirements for the scheme in use.
</t>
<t>In the OAUTH-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 query parameters of the tunneled HTTP request. 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 authentication scheme MUST carry the user ID to be used as the
authorization identity (identity to act as). The server
MUST use that ID as the user being authorized, that is the user assertion
we accept and not other information such as from the URL or
"User:" header. </t>
<t> The server responds to failed authentication by sending discovery information
in an HTTP style response with the HTTP status code set to 401, and then
failing the authentication.
</t>
<t>If channel binding is in use and the channel
binding fails the server responds with a minimal HTTP response without discovery
information and the HTTP 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="Mapping to SASL Identities">
<t> Some OAuth mechanisms can provide both an authorization identity and an
authentication identity. An example of this is OAuth 1.0a <xref target="RFC5849"/> where
the consumer key (oauth_consumer_key) identifies the entity using to token which equates to the
SASL authentication identity, and is authenticated using the shared secret. The
authorization identity in the OAuth 1.0a case is carried in the token (per the requirement
above), which SHOULD validated independently. The server MAY use a consumer key or
other comparable identity in the OAuth authorization scheme as the SASL authentication identity.
If an appropriate authentication identity is not available the server MUST use the
identity asserted in the token.</t>
</section>
<section title="Discovery Information">
<t>The server MUST send discovery information in response to a failed authentication
exchange or a request with an empty Authorization header. If discovery information is
returned it MUST include an authentication
endpoint appropriate for the user. If the "User" header is present the discovery
information MUST be for that user. Discovery information is provided by the server to the
client to allow a client to discover the appropriate OAuth authentication and token
endpoints. The client then uses that information to obtain the access token needed for
OAuth authentication. The client SHOULD cache and re-use the user specific discovery
information for service endpoints. </t>
<t>Discovery information makes use of both the WWW-Authenticate header as defined
in HTTP Authentication: Basic and Digest Access Authentication <xref target="RFC2617"/> and Link headers as
defined in <xref target="RFC5988"/>. The following elements are defined for discovery information:
<list style="hanging">
<t hangText="WWW-Authenticate"> A WWW-Authenticate header for each authentication scheme
supported by the server. Authentication scheme names are case
insensitive. The following <xref target="RFC2617"/> authentication
parameters are defined:
<list style="hanging">
<t hangText="realm">REQUIRED -- (as defined by RFC2617)</t>
<t hangText="scope">OPTIONAL -- A quoted string. This provides the
client an OAuth 2 scope known to be valid for the resource.</t>
</list>
</t>
<t hangText="oauth2-authenticator"> An <xref target="RFC5988"/> Link header specifying
the <xref target="I-D.ietf-oauth-v2"/> authentication endpoint. This link has an
OPTIONAL link-extension "scheme", if included this link applies ONLY to the
specified scheme.
</t>
<t hangText="oauth2-token"> An <xref target="RFC5988"/> Link header specifying
the <xref target="I-D.ietf-oauth-v2"/> token endpoint. This link has an
OPTIONAL link-extension "scheme", if included this link applies ONLY to the
specified scheme.
</t>
<t hangText="oauth-initiate"> (Optional) An <xref target="RFC5988"/> Link header specifying
the OAuth1.0a <xref target="RFC5849"/> initiation endpoint. The server MUST send this if
"OAuth" is included in the supported list of HTTP authentication schemes for the
server.
</t>
<t hangText="oauth-authorize"> (Optional) An <xref target="RFC5988"/> Link header specifying
the OAuth1.0a <xref target="RFC5849"/> authentication endpoint. The server MUST send this if
"OAuth" is included in the supported list of HTTP authentication schemes for the
server.
</t>
<t hangText="oauth-token"> (Optional) An <xref target="RFC5988"/> Link header specifying
the OAuth1.0a <xref target="RFC5849"/> token endpoint. The server MUST send this if
"OAuth" is included in the supported list of HTTP authentication schemes for the
server. This link type has one link-extension "grant-types" which is a space
separated list of the OAuth 2.0 grant types that can be used at the token
endpoint to obtain a token.
</t>
</list>
</t>
<t>Usage of the URLs provided in the discovery information is defined in the relevant
specifications. If the server supports multiple authenticators the discovery information
returned for unknown users MUST be consistent with the discovery information for known
users to prevent user enumeration. The OAuth 2.0 specification <xref
target="I-D.ietf-oauth-v2"/> supports multiple types of authentication schemes and the server
MUST specify at least one supported authentication scheme in the discovery information. The server
MAY support multiple schemes and MAY support schemes not listed in the discovery
information.</t>
<t>If the resource server provides a scope the client SHOULD 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 must be defined by the resource owner and provided in service
documentation (which is beyond the scope of this memo).
</t>
</section>
<section title="Use of Signature Type Authorization">
<t>This mechanism supports authorization using signatures, which requires that both client and
server construct the string to be signed. OAuth 2 is designed for
authentication/authorization to access specific URIs. SASL is designed for user authentication,
and has no facility for being more specific. In this mechanism we require an HTTP style
format specifically to support signature type authentication, but this is extremely
limited. The HTTP style request is limited to a path of "/". This
mechanism is in the SASL model, but is
designed 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 MAC specification <xref target="I-D.ietf-oauth-v2-http-mac"/>
as a starting point, on an IMAP server running on port 143 and given
the MAC style authorization request (with long lines wrapped for readability) below:
<figure>
<artwork><![CDATA[
GET / HTTP/1.1
Host: server.example.com
User: user@example.com
Authorization: MAC token="h480djs93hd8",timestamp="137131200",
nonce="dj83hs9s",signature="YTVjyNSujYs1WsDurFnvFi4JK6o="
]]></artwork>
</figure>
</t>
<t>The normalized request string would be constructed per the MAC specification <xref
target="I-D.ietf-oauth-v2-http-mac" />. In this example the normalized
request string with the new line separator character is represented by
"\n" for display purposes only would be:<figure>
<artwork><![CDATA[
h480djs93hi8\n
137131200\n
dj83hs9s\n
\n
GET\n
server.example.com\n
143\n
/\n
\n
]]></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>The SASL OAuth mechanism is also a GSS-API mechanism and the messages
described in <xref target="SASL-OAUTH"/> are the same, but
<list style="numbers">
<t>the GS2 header on the client's
first message is excluded when OAUTH is used as a GSS-API
mechanism, and</t>
<t>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 OID for OAuth is [[TBD: IANA]].</t>
<t>OAuth 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, as discussed in
<xref target="RFC6125"/>.</t>
<t>The OAuth mechanism does 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 supports 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 example illustrate exchanges between an IMAP client and an IMAP server.</t>
<section title="Successful Bearer Token Exchange">
<t>This example shows a successful OAuth 2.0 bearer token exchange with an initial client
response. Note that line breaks are inserted for readability.</t>
<t>
<figure>
<artwork><![CDATA[
S: * IMAP4rev1 Server Ready
C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8gSFRUUC8xLjENCkhvc3Q6IGltYXAuZXhhbXBs
ZS5jb20NCkF1dGhvcml6YXRpb246IEJFQVJFUiAidkY5ZGZ0NHFtVGMyTnZiM1J
sY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09Ig0KDQo=
S: +
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 is: <figure>
<artwork><![CDATA[
GET / HTTP/1.1
Host: imap.example.com
Authorization: BEARER "vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg=="
]]></artwork>
</figure>
</t>
<t>The line containing just a "+" and a space is an empty response from the server. This response contains
discovery information, and in the success case no discovery information is necessary so the
response is empty. Like other messages, and in accordance with the IMAP SASL binding, the
empty response is base64-encoded. </t>
</section>
<!-- ******************************************************************** -->
<section title="MAC Authentication with Channel Binding">
<t>This example shows a channel binding failure. The example sends the same
request as above, but in the context of an OAUTH-PLUS exchange the channel binding
information is missing. Note that line breaks are inserted for
readability.</t>
<t>
<figure>
<artwork><![CDATA[
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE MAC R0VUIC8/Y2JkYXRhPSJTRzkzSUdKcFp5QnBjeUJoSUZSTVV5Q
m1hVzVoYkNCdFpYTnpZV2RsUHdvPSIgSFRUUC8xLjENCkhvc3Q6IHNlcnZlci5leGFtcG
xlLmNvbQ0KVXNlcjogdXNlckBleGFtcGxlLmNvbQ0KQXV0aG9yaXphdGlvbjogTUFDIHR
va2VuPSJoNDgwZGpzOTNoZDgiLHRpbWVzdGFtcD0iMTM3MTMxMjAwIixub25jZT0iZGo4
M2hzOXMiLHNpZ25hdHVyZT0iV1c5MUlHMTFjM1FnWW1VZ1ltOXlaV1F1SUFvPSINCg0K
S: +
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 is: <figure>
<artwork><![CDATA[
GET /?cbdata="SG93IGJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=" HTTP/1.1
Host: server.example.com
User: user@example.com
Authorization: MAC token="h480djs93hd8",timestamp="137131200",
nonce="dj83hs9s",signature="WW91IG11c3QgYmUgYm9yZWQuIAo="
]]></artwork>
</figure>
</t>
<t>The line containing just a "+" and a space is an empty response from the server. This response contains
discovery information, and in the success case no discovery information is necessary so the
response is empty. Like other messages, and in accordance with the IMAP SASL binding, the
empty response is base64-encoded.
</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 discovery information. Note that line breaks are inserted for
readability.</t>
<t>
<figure>
<artwork><![CDATA[
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8gSFRUUC8xLjENClVzZXI6IHNjb290ZXJAYW
x0YXZpc3RhLmNvbQ0KSG9zdDogaW1hcC55YWhvby5jb20NCkF1dGhlbnRpY2F0ZT
ogDQoNCg==
S: + SFRUUC8xLjEgNDAxIFVuYXV0aG9yaXplZA0KV1dXLUF1dGhlbnRpY2F0ZTogQk
VBUkVSIHJlYWxtPSJleGFtcGxlLmNvbSINCkxpbms6IDxodHRwczovL2xvZ2luLn
lhaG9vLmNvbS9vYXV0aD4gcmVsPSJvYXV0aDItYXV0aGVudGljYXRvciIgIA0KTG
luazogPGh0dHBzOi8vbG9naW4ueWFob28uY29tL29hdXRoPiByZWw9Im91YXRoMi
10b2tlbiINCg0K
S: t1 NO SASL authentication failed
]]></artwork>
</figure>
</t>
<t> The decoded initial client response is: <figure>
<artwork><![CDATA[
GET / HTTP/1.1
User: alice@example.com
Host: imap.example.com
Authorization:
]]></artwork>
</figure>
</t>
<t> The decoded server discovery response is: <figure>
<artwork><![CDATA[
HTTP/1.1 401 Unauthorized
WWW-Authenticate: BEARER realm="example.com"
Link: <https://login.example.com/oauth> rel="oauth2-authenticator"
Link: <https://login.example.com/oauth> rel="oauth2-token"
]]></artwork>
</figure>
</t>
</section>
<!-- ******************************************************************** -->
<section title="Failed Channel Binding">
<t>This example shows a channel binding failure in a discovery request.
The channel binding information is empty. Note that line breaks are inserted for
readability.</t>
<t>
<figure>
<artwork><![CDATA[
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8/Y2JkYXRhPSIiIEhUVFAvMS4xDQpVc2VyOi
BhbGljZUBleGFtcGxlLmNvbQ0KSG9zdDogaW1hcC5leGFtcGxlLmNvbQ0KQXV0aG
9yaXphdGlvbjoNCg0K
S: + SFRUUC8xLjEgNDEyIFByZWNvbmRpdGlvbiBGYWlsZWQNCg0KDQo=
S: t1 NO SASL authentication failed
]]></artwork>
</figure>
</t>
<t> The decoded initial client response is: <figure>
<artwork><![CDATA[
GET /?cbdata="" HTTP/1.1
User: alice@example.com
Host: imap.example.com
Authorization:
]]></artwork>
</figure>
</t>
<t> The decoded server response is: <figure>
<artwork><![CDATA[
HTTP/1.1 412 Precondition Failed
]]></artwork>
</figure>
</t>
</section>
<!-- ******************************************************************** -->
</section>
<!-- ******************************************************************** -->
<section title="Security Considerations">
<t> This mechanism does not provide a security layer, but does provide a provision for
channel binding. The OAuth 2 specification <xref
target="I-D.ietf-oauth-v2"/> allows for a variety of usages, and the security properties
of these profiles vary. The usage of bearer tokens, for example, provide security features
similar to cookies. Applications using this mechanism SHOULD exercise the same level of care
using this mechanism as they would in using the SASL PLAIN mechanism. In
particular, TLS 1.2 or an equivalent secure channel MUST be implemented and its
usage is RECOMMENDED.
</t>
<t> Channel binding in this mechanism has different properties based on the authentication
scheme used. Channel binding to TLS with a
bearer token provides only a binding to the TLS layer. Authentication schemes like MAC
tokens have a signature over the channel binding information. These provide additional
protection against a man in the middle attacks, and the MAC authorization header is bound to the
channel and only valid in that context.
</t>
<t> It is possible that SASL will be authenticating a connection and the life of that
connection may outlast the life of the token used to authenticate
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>An OAuth credential is not equivalent to the password or primary account
credential. There are protocols like XMPP that allow actions like change
password. The server SHOULD ensure that actions taken in the authenticated
channel are appropriate to the strength of the presented credential.
</t>
<t> It is possible for an application server running on Evil.example.com to tell a client to
request a token from Good.example.org. A client following these instructions will pass a
token from Good to Evil. This is by design, since it is possible that Good and Evil are
merely names, not descriptive, and that this is an innocuous activity between cooperating
two servers in different domains. For instance, a site might operate their authentication
service in-house, but outsource their mail systems to an external entity. </t>
<t>Tokens have a lifetime associated with them. Reducing both the lifetime of a token provides security benefits in case that tokens leak. In addition a previously obtained
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="IANA Considerations">
<section title="SASL Registration">
<t> The IANA is requested to register the following SASL profile: <list style="empty">
<t>SASL mechanism profile: OAUTH</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: OAUTH-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 this GSS mechanism
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 title="Link Type Registration">
<t> Pursuant to <xref target="RFC5988"/> The following link type registrations
[[will be]] registered by mail to link-relations@ietf.org.
</t>
<section title="OAuth 2 Authentication Endpoint">
<t>
<list style='symbols'>
<t>
Relation Name: oauth2-authenticator
</t>
<t>
Description: An OAuth 2.0 authentication endpoint.
</t>
<t>
Reference:
</t>
<t>
Notes: This link type indicates an OAuth 2.0 authentication endpoint
that can be used for user authentication/authorization for the endpoint
providing the link.
</t>
<t>
Application Data: [optional]
</t>
</list>
</t>
</section>
<section title="OAuth 2 Token Endpoint">
<t>
<list style='symbols'>
<t>Relation Name: oauth2-token</t>
<t>
Description: The OAuth token endpoint used to get tokens for access.
</t>
<t>
Reference:
</t>
<t>
Notes: The OAuth 2.0 token endpoint to be used for obtaining tokens
to access the endpoint providing the link.
</t>
<t>
Application Data: This link type has one link-extension "grant-types",
which is the OAuth 2.0 grant types that can be used at the token endpoint
to obtain a token. This is not an exclusive list, it provides a hint
to the application of what SHOULD be valid. A token endpoint MAY support
additional grant types not advertised by a resource endpoint.
</t>
</list>
</t>
</section>
<section title="OAuth 1.0a Request Initiation Endpoint">
<t>
<list style='symbols'>
<t>Relation Name: oauth-initiate</t>
<t>
Description: The OAuth 1.0a request initiation endpoint used to get tokens for access.
</t>
<t>Reference: </t>
<t>
Notes: The OAuth 1.0a endpoint used to initiate the sequence, this temporary
request is what the user approves to grant access to the resource.
</t>
<t>Application Data: </t>
</list>
</t>
</section>
<section title="OAuth 1.0a Authorization Endpoint">
<t>
<list style='symbols'>
<t>Relation Name: oauth-authorize</t>
<t>
Description: The OAuth 1.0a authorization endpoint used to approve an access request.
</t>
<t>Reference: </t>
<t>
Notes:
</t>
<t>Application Data: </t>
</list>
</t>
</section>
<section title="OAuth 1.0a Token Endpoint">
<t>
<list style='symbols'>
<t>Relation Name: oauth-token</t>
<t>
Description: The OAuth 1.0a token endpoint used to get tokens for access.
</t>
<t>Reference: </t>
<t>
Notes:
</t>
<t>Application Data: </t>
</list>
</t>
</section>
</section>
</section>
<!-- ******************************************************************** -->
<section title='Appendix A -- Document History'>
<t>
[[ to be removed by RFC editor before publication as an RFC ]]
</t>
<t>
-04
</t>
<t>
<list style='symbols'>
<t>
Editorial clean-up and text in introduction improved.
</t>
<t>
Added GSS-API support
</t>
</list>
</t>
<t>
-03
</t>
<t>
<list style='symbols'>
<t>
Fixing channel binding, not tls-unique specific. Also defining how the CB data is
properly generated.
</t>
<t>
Various small editorial changes and embarassing spelling fixes.
</t>
</list>
</t>
<t>
-02
</t>
<t>
<list style='symbols'>
<t>
Filling out Channel Binding
</t>
<t>
Added text clarifying how to bind to the 2 kinds of SASL identities.
</t>
</list>
</t>
<t>
-01
</t>
<t>
<list style='symbols'>
<t>
Bringing this into line with draft 12 of the core spec, the
bearer token spec, and references the MAC token spec
</t>
<t>
Changing discovery over to using the Link header construct from RFC5988.
</t>
<t>
Added the seeds of channel binding.
</t>
</list>
</t>
<t>
-00
</t>
<t>
<list style='symbols'>
<t>
Initial revision
</t>
</list>
</t>
</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.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.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.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/bibxml3/reference.I-D.ietf-oauth-v2.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-oauth-v2-bearer.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-oauth-v2-http-mac.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.hammer-hostmeta.xml' ?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.jones-simple-web-discovery.xml' ?>
</references>
</back>
</rfc>
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