One document matched: draft-richer-oauth-chain-00.xml
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<rfc category="std" docName="draft-richer-oauth-chain" ipr="trust200902">
<front>
<title abbrev="oauth2-chain">A Method of Bearer Token Redelegation and
Chaining for OAuth 2</title>
<author fullname="Justin Richer" initials="J." surname="Richer">
<organization>The MITRE Corporation</organization>
<address>
<postal>
<street>202 Burlington Rd.</street>
<city>Bedford</city>
<code>01821</code>
<region>Massachusetts</region>
<country>USA</country>
</postal>
<phone>+1-781-271-8176</phone>
<facsimile></facsimile>
<email>jricher@mitre.org</email>
</address>
</author>
<date day="07" month="September" year="2012" />
<keyword>Draft</keyword>
<abstract>
<t>This document provides a method for a resource server to present a
token that it has received from a client back to its authorization
server for the purposes of receiving a derivative token for use on
another resource server in order to chain together service requests.</t>
</abstract>
<note title="Requirements Language">
<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">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Service Chaining">
<t>The OAuth2 Authorization protocol provides methods for clients to
request tokens from authorization servers on behalf of resource owners
for use at resource servers. However, there are no provisions for a
resource server to act as a client itself for another resource server, a
practice known generally as service chaining. Typically, the services
involved in the chain are within a single security domain, and with
OAuth they would be using a single Authorization Server.</t>
<t>For services using the OAuth2 Bearer token profile, it is possible
for anyone holding the token to call any other service that accepts the
token. While this is functional, it is bad practice since the token is
knowingly being re-used by someone other than the client to which it was
issued. Since the same token is used in each step, this approach also
does not allow for attenuation of rights as the chain progresses.</t>
<t>Using a new form of grant_type, this specification presents such
chained resource servers with an alternative approach that takes
advantage of the simplicity and structure of the OAuth protocol by
providing a means for any resource server to present the token it has
been accessed with back to the authorization server in order to exchange
it for a token of equal or lesser strength for use with another resource
server. In this way, the original access token which has been delegated
to the client can be redelegated to a secondary service.</t>
<t>This approach differs slightly from the Refresh Token described in
the OAuth 2 Core. With a Refresh Token, the Client presents the token to
the authorization server to get a new Access Token without involving the
Resource Owner. With a redelegated Access Token, as described in this
document, the Resource Server presents the Access Token which was
provided to it by a Client in order to get a secondary Access Token.</t>
<section title="Abbreviations Used In This Document">
<t><list style="hanging">
<t hangText="AS">Authorization Server</t>
<t hangText="C">Client</t>
<t hangText="RO">Resource Owner</t>
<t hangText="RS1">Primary Resource Server, initially called by C
on behalf of RO</t>
<t hangText="RS2">Chained Resource Server, called by RS1 to
fulfill request from C</t>
<t hangText="AT1">Bearer Access Token granted by AS to C to access
RS1 on behalf of RO</t>
<t hangText="AT2">Bearer Access Token granted by AS to RS1 to
access RS2 on behalf of RO</t>
</list></t>
</section>
</section>
<section title="Protocol Description">
<t>The process begins with any standard OAuth2 protocol flow, where the
client obtains AT1 from the AS.</t>
<figure>
<preamble>The beginning of the process is standard OAuth2 §1.2
using any legal OAuth2 grant type to obtain the AT1.</preamble>
<artwork><![CDATA[
+--------+ +-------------+
| |--(A)->| Resource |
| | | Owner |
| |<-(B)--| (RO) |
| | +-------------+
| |
| | +---------------+
| |--(C)----------------------->| Authorization |
| Client | | Server |
| |<-(D)------------------------| (AS) |
| | | |
| | | |
| | +-------------+ | |
| |--(E)->| Primary |--(F)->| |
| | | Resource | | |
| | | Server |<-(G)--| |
| | | (RS1) | +---------------+
| | | |
| | | | +---------------+
| | | |--(H)->| Chained |
| | | | | Resource |
| | | | | Server |
| | | |<-(I)--| (RS2) |
| |<-(J)--| | +---------------+
+--------+ +-------------+
]]></artwork>
</figure>
<t><list style="hanging">
<t hangText="(A)">Client requests authorization from Resource
Owner</t>
<t hangText="(B)">Client receives authorization from the Resource
Owner using any valid OAuth2 grant type</t>
<t hangText="(C)">Client requests AT1 from the AS by authenticating
with the AS and presenting the authorization grant obtained in
(B)</t>
<t hangText="(D)">AS authenticates the Client and issues access
token AT1 for use at RS1</t>
<t hangText="(E)">Client presents access token AT1 to RS1 to access
a protected resource</t>
<t hangText="(F)">RS1 needs to access RS2 to fulfill this request,
makes a call to the Token Endpoint on the AS using the redelegate
grant_type</t>
<t hangText="(G)">AS validates AT1 and issues a token AT2 for use by
RS1 against RS2, where the rights assigned to AT2 are a subset of
those assigned to AT1</t>
<t hangText="(H)">RS1 presents AT2 to RS2 to access a protected
resource</t>
<t hangText="(I)">RS2 validates token AT2 and returns the protected
resource to RS1</t>
<t hangText="(J)">Client receives protected resource from RS1,
including information sourced from RS2</t>
</list>Steps A-E and J are standard OAuth2 and OAuth2 Bearer tokens
involving token AT1. As such, the Client MAY make use of any OAuth2
grant type, such as authorization_code, implicit, client_credentials,
password, assertion, or even the redelegation protocol defined in this
document. Steps F-G are described in section 3 of this document. Steps
H-I are standard OAuth2 Bearer token usage, but using the delegated
token AT2.</t>
<t>The means by which the Resource Servers validate the Access Tokens is
out of scope of this specification. At the time of this writing, there
are two main approaches found in practice: token introspection and
structured tokens.</t>
</section>
<section title="Redelegation Grant Type">
<t>The Resource Server RS1 makes a request using the Access Token that
was presented to it in order to obtain a new Access Token.</t>
<section title="Redelegate Request">
<t>To access RS2, RS1 makes a POST request to the Authorization
Server's Token Endpoint with the following parameters:</t>
<t><list style="hanging">
<t hangText="grant_type">REQUIRED. Value MUST be set to
"urn:ietf:params:oauth:grant_type:redelegate".</t>
<t hangText="token">REQUIRED The token that was presented to the
resource server by the client, referred to as AT1 in the protocol
flow, an OAuth2 Bearer token</t>
<t hangText="scope">OPTIONAL a space-separated list of strings as
described in OAuth 2. If present, this scope list MUST be equal to
or lesser than the scopes incorporated in AT1. The AS MUST issue a
token of equal or lesser scope than the token above.</t>
</list>The Authorization Server MAY require RS1 to have registered
as a client on its own behalf. In this case, RS1 MUST present its
client credentials as described in OAuth2 Core.</t>
</section>
<section title="Access Token Response">
<t>If the request is valid and authorized, the AS issues an access
token, referred to as AT2 in the protocol flow, as described in OAuth2
Core. As this access token is bound to an existing access token, the
authorization server MUST NOT issue a refresh token. If the request
failed, the authorization server returns an error response as
described in OAuth2 Core.</t>
<figure>
<artwork><![CDATA[
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"access_token":"2YotnFZFEjr1zCsicMWpAA",
"token_type":"example",
"expires_in":3600,
"example_parameter":"example_value"
}
]]></artwork>
</figure>
</section>
<section title="Error Response">
<t>If the token request is not valid, such as the access token
presented does not allow for redelegation, the AS returns an error
response as described in OAuth2 Core.</t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>[Registration into the OAuth registry for
urn:ietf:params:oauth:grant_type:redelegate]</t>
<t>Note to RFC Editor: this section may be removed on publication as an
RFC.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>A resource server engaging in service chaining and token redelegation
SHOULD request a redelegated token with only the minimum set of scopes
necessary for calling downstream services.</t>
<t>A resource server MUST indicate in service documentation the full set
of scopes required for accessing the full service chain. A redelegation
request MUST NOT request escalated privileges without involving the
resource owner in a new authorization grant.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>This work has grown from discussions with Paul Nguyen and Stephen
Moore, both of MITRE.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
</references>
<references title="Informative References">
<reference anchor="InfRef">
<front>
<title></title>
<author>
<organization></organization>
</author>
<date year="2004" />
</front>
</reference>
</references>
<section title="Standardization of Scopes">
<t>The OAuth2 specification explicitly leaves the definition of scopes
to the Authorization Server and Protected Resource to agree upon.
However, in the course of redelegation, it is sometimes desirable to
have a scope value related to the redelegation permission itself. It is
RECOMMENDED to use a scope value of "redelegate" if possible.</t>
</section>
</back>
</rfc>
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