wdiff rfc8693.original rfc8693.txt

OAuth Working Group

Internet Engineering Task Force (IETF) M. Jones
Internet-Draft
Request for Comments: 8693 A. Nadalin
Intended status:
Category: Standards Track Microsoft
Expires: January 21, 2020
ISSN: 2070-1721 B. Campbell, Ed.
Ping Identity
J. Bradley
Yubico
C. Mortimore
Salesforce
July 20, 2019
Visa
January 2020

OAuth 2.0 Token Exchange
draft-ietf-oauth-token-exchange-19

Abstract

This specification defines a protocol for an HTTP- and JSON- based JSON-based
Security Token Service (STS) by defining how to request and obtain
security tokens from OAuth 2.0 authorization servers, including
security tokens employing impersonation and delegation.

Status of This Memo

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This Internet-Draft will expire on January 21, 2020.
https://www.rfc-editor.org/info/rfc8693.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Delegation vs. Impersonation Semantics . . . . . . . . . 4
1.2. Requirements Notation and Conventions . . . . . . . . . . 6
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Token Exchange Request and Response . . . . . . . . . . . . . 6
2.1. Request . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1. Relationship Between between Resource, Audience Audience, and Scope . . 9
2.2. Response . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.1. Successful Response . . . . . . . . . . . . . . . . . 9
2.2.2. Error Response . . . . . . . . . . . . . . . . . . . 11
2.3. Example Token Exchange . . . . . . . . . . . . . . . . . 11
3. Token Type Identifiers . . . . . . . . . . . . . . . . . . . 13
4. JSON Web Token Claims and Introspection Response Parameters . 15
4.1. "act" (Actor) Claim . . . . . . . . . . . . . . . . . . . 15
4.2. "scope" (Scopes) Claim . . . . . . . . . . . . . . . . . 17
4.3. "client_id" (Client Identifier) Claim . . . . . . . . . . 18
4.4. "may_act" (Authorized Actor) Claim . . . . . . . . . . . 18
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 20
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
7.1. OAuth URI Registration . . . . . . . . . . . . . . . . . 20
7.1.1. Registry Contents . . . . . . . . . . . . . . . . . . 20
7.2. OAuth Parameters Registration . . . . . . . . . . . . . . 21
7.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 21
7.3. OAuth Access Token Type Registration . . . . . . . . . . 22
7.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 22
7.4. JSON Web Token Claims Registration . . . . . . . . . . . 22
7.4.1. Registry Contents . . . . . . . . . . . . . . . . . . 22
7.5. OAuth Token Introspection Response Registration . . . . . 23
7.5.1. Registry Contents . . . . . . . . . . . . . . . . . . 23
7.6. OAuth Extensions Error Registration . . . . . . . . . . . 23
7.6.1. Registry Contents . . . . . . . . . . . . . . . . . . 23
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.1. Normative References . . . . . . . . . . . . . . . . . . 24
8.2. Informative References . . . . . . . . . . . . . . . . . 24
Appendix A. Additional Token Exchange Examples . . . . . . . . . 26
A.1. Impersonation Token Exchange Example . . . . . . . . . . 26
A.1.1. Token Exchange Request . . . . . . . . . . . . . . . 26
A.1.2. Subject Token Claims . . . . . . . . . . . . . . . . 26
A.1.3. Token Exchange Response . . . . . . . . . . . . . . . 27
A.1.4. Issued Token Claims . . . . . . . . . . . . . . . . . 27
A.2. Delegation Token Exchange Example . . . . . . . . . . . . 28
A.2.1. Token Exchange Request . . . . . . . . . . . . . . . 28
A.2.2. Subject Token Claims . . . . . . . . . . . . . . . . 29
A.2.3. Actor Token Claims . . . . . . . . . . . . . . . . . 29
A.2.4. Token Exchange Response . . . . . . . . . . . . . . . 29
A.2.5. Issued Token Claims . . . . . . . . . . . . . . . . . 30
Appendix B.
Acknowledgements . . . . . . . . . . . . . . . . . . 31
Appendix C. Document History . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35

1. Introduction

A security token is a set of information that facilitates the sharing
of identity and security information in heterogeneous environments or
across security domains. Examples of security tokens include JSON
Web Tokens (JWTs) [JWT] and SAML Security Assertion Markup Language (SAML)
2.0 Assertions assertions [OASIS.saml-core-2.0-os]. Security tokens are
typically signed to achieve integrity and sometimes also encrypted to
achieve confidentiality. Security tokens are also sometimes
described as
Assertions, assertions, such as in [RFC7521].

A Security Token Service (STS) is a service capable of validating
security tokens provided to it and issuing new security tokens in
response, which enables clients to obtain appropriate access
credentials for resources in heterogeneous environments or across
security domains. Web Service clients have used WS-Trust [WS-Trust]
as the protocol to interact with an STS for token exchange. While
WS-Trust uses XML and SOAP, the trend in modern Web development has
been towards RESTful (Representational State Transfer) patterns and
JSON. The OAuth 2.0 Authorization Framework [RFC6749] and OAuth 2.0
Bearer Tokens [RFC6750] have emerged as popular standards for
authorizing third-party applications' access to HTTP and RESTful
resources. The conventional OAuth 2.0 interaction involves the
exchange of some representation of resource owner authorization for
an access token, which has proven to be an extremely useful pattern
in practice. However, its input and output are somewhat too
constrained as is to fully accommodate a security token exchange
framework.

This specification defines a protocol extending OAuth 2.0 that
enables clients to request and obtain security tokens from
authorization servers acting in the role of an STS. Similar to OAuth
2.0, this specification focuses on client developer simplicity and
requires only an HTTP client and JSON parser, which are nearly
universally available in modern development environments. The STS
protocol defined in this specification is not itself RESTful (an STS
doesn't lend itself particularly well to a REST approach) but does
utilize communication patterns and data formats that should be
familiar to developers accustomed to working with RESTful systems.

A new grant type for a token exchange request and the associated
specific parameters for such a request to the token endpoint are
defined by this specification. A token exchange response is a normal
OAuth 2.0 response from the token endpoint with a few additional
parameters defined herein to provide information to the client.

The entity that makes the request to exchange tokens is considered
the client in the context of the token exchange interaction.
However, that does not restrict usage of this profile to traditional
OAuth clients. An OAuth resource server, for example, might assume
the role of the client during token exchange in order to trade an
access token that it received in a protected resource request for a
new token that is appropriate to include in a call to a backend
service. The new token might be an access token that is more
narrowly scoped for the downstream service or it could be an entirely
different kind of token.

The scope of this specification is limited to the definition of a
basic request-and-response protocol for an STS-style token exchange
utilizing OAuth 2.0. Although a few new JWT claims are defined that
enable delegation semantics to be expressed, the specific syntax,
semantics
semantics, and security characteristics of the tokens themselves
(both those presented to the authorization server and those obtained
by the client) are explicitly out of scope scope, and no requirements are
placed on the trust model in which an implementation might be
deployed. Additional profiles may provide more detailed requirements
around the specific nature of the parties and trust involved, such as
whether signing and/or encryption of tokens is needed or if proof-of-
possession style
possession-style tokens will be required or issued; however, issued. However, such
details will often be policy decisions made with respect to the
specific needs of individual deployments and will be configured or
implemented accordingly.

The security tokens obtained may be used in a number of contexts, the
specifics of which are also beyond the scope of this specification.

1.1. Delegation vs. Impersonation Semantics

One common use case for an STS (as alluded to in the previous
section) is to allow a resource server A to make calls to a backend
service C on behalf of the requesting user B. Depending on the local
site policy and authorization infrastructure, it may be desirable for
A to use its own credentials to access C along with an annotation of
some form that A is acting on behalf of B ("delegation"), ("delegation") or for A to
be granted a limited access credential to C but that continues to
identify B as the authorized entity ("impersonation"). Delegation
and impersonation can be useful concepts in other scenarios involving
multiple participants as well.

When principal A impersonates principal B, A is given all the rights
that B has within some defined rights context and is
indistinguishable from B in that context. Thus, when principal A
impersonates principal B, then insofar as any entity receiving such a
token is concerned, they are actually dealing with B. It is true
that some members of the identity system might have awareness that
impersonation is going on, but it is not a requirement. For all
intents and purposes, when A is impersonating B, A is B within the
context of the rights authorized by the token. A's ability to
impersonate B could be limited in scope or time, or even with a one-
time-use restriction, whether via the contents of the token or an
out-of-band mechanism.

Delegation semantics are different than impersonation semantics,
though the two are closely related. With delegation semantics,
principal A still has its own identity separate from B B, and it is
explicitly understood that while B may have delegated some of its
rights to A, any actions taken are being taken by A representing B.
In a sense, A is an agent for B.

Delegation and impersonation are not inclusive of all situations.
When a principal is acting directly on its own behalf, for example,
neither delegation nor impersonation are in play. They are, however,
the more common semantics operating for token exchange and, as such,
are given more direct treatment in this specification.

Delegation semantics are typically expressed in a token by including
information about both the primary subject of the token as well as
the actor to whom that subject has delegated some of its rights.
Such a token is sometimes referred to as a composite token because it
is composed of information about multiple subjects. Typically, in
the request, the "subject_token" represents the identity of the party
on behalf of whom the token is being requested while the
"actor_token" represents the identity of the party to whom the access
rights of the issued token are being delegated. A composite token
issued by the authorization server will contain information about
both parties. When and if a composite token is issued is at the
discretion of the authorization server and applicable policy and
configuration.

The specifics of representing a composite token and even whether or
not such a token will be issued depend on the details of the
implementation and the kind of token. The representations of
composite tokens that are not JWTs are beyond the scope of this
specification. The "actor_token" request parameter, however, does
provide a means for providing information about the desired actor actor,
and the JWT "act" claim can provide a representation of a chain of
delegation.

1.2. Requirements Notation and Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

1.3. Terminology

This specification uses the terms "access token type", "authorization
server", "client", "client identifier", "resource server", "token
endpoint", "token request", and "token response" defined by OAuth 2.0
[RFC6749], and the terms "Base64url Encoding", "Claim", and "JWT
Claims Set" defined by JSON Web Token (JWT) [JWT].

2. Token Exchange Request and Response

2.1. Request

A client requests a security token by making a token request to the
authorization server's token endpoint using the extension grant type
mechanism defined in Section 4.5 of [RFC6749].

Client authentication to the authorization server is done using the
normal mechanisms provided by OAuth 2.0. Section 2.3.1 of [RFC6749]
defines password-based authentication of the client, however, client
authentication is extensible and other mechanisms are possible. For
example, [RFC7523] defines client authentication using bearer JSON
Web Tokens (JWTs) [JWT]. The supported methods of client
authentication and whether or not to allow unauthenticated or
unidentified clients are deployment decisions that are at the
discretion of the authorization server. Note that omitting client
authentication allows for a compromised token to be leveraged via an
STS into other tokens by anyone possessing the compromised token.
Thus
Thus, client authentication allows for additional authorization
checks by the STS as to which entities are permitted to impersonate
or receive delegations from other entities.

The client makes a token exchange request to the token endpoint with
an extension grant type using the HTTP "POST" method. The following
parameters are included in the HTTP request entity-body using the
"application/x-www-form-urlencoded" format with a character encoding
of UTF-8 as described in Appendix B of RFC6749 [RFC6749].

grant_type
REQUIRED. The value "urn:ietf:params:oauth:grant-type:token-
exchange" indicates that a token exchange is being performed.

resource
OPTIONAL. A URI that indicates the target service or resource
where the client intends to use the requested security token.
This enables the authorization server to apply policy as
appropriate for the target, such as determining the type and
content of the token to be issued or if and how the token is to be
encrypted. In many cases, a client will not have knowledge of the
logical organization of the systems with which it interacts and
will only know a URI of the service where it intends to use the
token. The "resource" parameter allows the client to indicate to
the authorization server where it intends to use the issued token
by providing the location, typically as an https URL, in the token
exchange request in the same form that will be used to access that
resource. The authorization server will typically have the
capability to map from a resource URI value to an appropriate
policy. The value of the "resource" parameter MUST be an absolute
URI, as specified by Section 4.3 of [RFC3986], which that MAY include a
query component and MUST NOT include a fragment component.
Multiple "resource" parameters may be used to indicate that the
issued token is intended to be used at the multiple resources
listed. See [I-D.ietf-oauth-resource-indicators] [OAUTH-RESOURCE] for additional background and uses
of the "resource" parameter.

audience
OPTIONAL. The logical name of the target service where the client
intends to use the requested security token. This serves a
purpose similar to the "resource" parameter, parameter but with the client
providing a logical name for the target service. Interpretation
of the name requires that the value be something that both the
client and the authorization server understand. An OAuth client
identifier, a SAML entity identifier [OASIS.saml-core-2.0-os], and
an OpenID Connect Issuer Identifier [OpenID.Core], [OpenID.Core] are examples of
things that might be used as "audience" parameter values.
However, "audience" values used with a given authorization server
must be unique within that server, server to ensure that they are properly
interpreted as the intended type of value. Multiple "audience"
parameters may be used to indicate that the issued token is
intended to be used at the multiple audiences listed. The
"audience" and "resource" parameters may be used together to
indicate multiple target services with a mix of logical names and
resource URIs.

scope
OPTIONAL. A list of space-delimited, case-sensitive strings, as
defined in Section 3.3 of [RFC6749], that allow the client to
specify the desired scope of the requested security token in the
context of the service or resource where the token will be used.
The values and associated semantics of scope are service specific
and expected to be described in the relevant service
documentation.

requested_token_type
OPTIONAL. An identifier, as described in Section 3, for the type
of the requested security token. If the requested type is
unspecified, the issued token type is at the discretion of the
authorization server and may be dictated by knowledge of the
requirements of the service or resource indicated by the
"resource" or "audience" parameter.

subject_token
REQUIRED. A security token that represents the identity of the
party on behalf of whom the request is being made. Typically, the
subject of this token will be the subject of the security token
issued in response to the request.

subject_token_type
REQUIRED. An identifier, as described in Section 3, that
indicates the type of the security token in the "subject_token"
parameter.

actor_token
OPTIONAL. A security token that represents the identity of the
acting party. Typically, this will be the party that is
authorized to use the requested security token and act on behalf
of the subject.

actor_token_type
An identifier, as described in Section 3, that indicates the type
of the security token in the "actor_token" parameter. This is
REQUIRED when the "actor_token" parameter is present in the
request but MUST NOT be included otherwise.

In processing the request, the authorization server MUST perform the
appropriate validation procedures for the indicated token type and,
if the actor token is present, also perform the appropriate
validation procedures for its indicated token type. The validity
criteria and details of any particular token are beyond the scope of
this document and are specific to the respective type of token and
its content.

In the absence of one-time-use or other semantics specific to the
token type, the act of performing a token exchange has no impact on
the validity of the subject token or actor token. Furthermore, the
exchange is a one-time event and does not create a tight linkage
between the input and output tokens, so that (for example) while the
expiration time of the output token may be influenced by that of the
input token, renewal or extension of the input token is not expected
to be reflected in the output token's properties. It may still be
appropriate or desirable to propagate token revocation token-revocation events.
However, doing so is not a general property of the STS protocol and
would be specific to a particular implementation, token type type, or
deployment.

2.1.1. Relationship Between between Resource, Audience Audience, and Scope

When requesting a token, the client can indicate the desired target
service(s) where it intends to use that token by way of the
"audience" and "resource" parameters, parameters as well as indicating indicate the desired
scope of the requested token using the "scope" parameter. The
semantics of such a request are that the client is asking for a token
with the requested scope that is usable at all the requested target
services. Effectively, the requested access rights of the token are
the cartesian Cartesian product of all the scopes at all the target services.

An authorization server may be unwilling or unable to fulfill any
token request request, but the likelihood of an unfulfillable request is
significantly higher when very broad access rights are being
solicited. As such, in the absence of specific knowledge about the
relationship of systems in a deployment, clients should exercise
discretion in the breadth of the access requested, particularly the
number of target services. An authorization server can use the
"invalid_target" error code, defined in Section 2.2.2, to inform a
client that it requested access to too many target services
simultaneously.

2.2. Response

The authorization server responds to a token exchange request with a
normal OAuth 2.0 response from the token endpoint, as specified in
Section 5 of [RFC6749]. Additional details and explanation are
provided in the following subsections.

2.2.1. Successful Response

If the request is valid and meets all policy and other criteria of
the authorization server, a successful token response is constructed
by adding the following parameters to the entity-body of the HTTP
response using the "application/json" media type, as specified by
[RFC8259], and an HTTP 200 status code. The parameters are
serialized into a JavaScript Object Notation (JSON) structure by
adding each parameter at the top level. Parameter names and string
values are included as JSON strings. Numerical values are included
as JSON numbers. The order of parameters does not matter and can
vary.

access_token
REQUIRED. The security token issued by the authorization server
in response to the token exchange request. The "access_token"
parameter from Section 5.1 of [RFC6749] is used here to carry the
requested token, which allows this token exchange protocol to use
the existing OAuth 2.0 request and response constructs defined for
the token endpoint. The identifier "access_token" is used for
historical reasons and the issued token need not be an OAuth
access token.

issued_token_type
REQUIRED. An identifier, as described in Section 3, for the
representation of the issued security token.

token_type
REQUIRED. A case-insensitive value specifying the method of using
the access token issued, as specified in Section 7.1 of [RFC6749].
It provides the client with information about how to utilize the
access token to access protected resources. For example, a value
of "Bearer", as specified in [RFC6750], indicates that the issued
security token is a bearer token and the client can simply present
it as is without any additional proof of eligibility beyond the
contents of the token itself. Note that the meaning of this
parameter is different from the meaning of the "issued_token_type"
parameter, which declares the representation of the issued
security token; the term "token type" is more typically used with
the aforementioned meaning as to
mean the structural or syntactical representation of the security
token, as it is in all "*_token_type" parameters in this
specification. If the issued token is not an access token or
usable as an access token, then the "token_type" value "N_A" is
used to indicate that an OAuth 2.0 "token_type" identifier is not
applicable in that context.

expires_in
RECOMMENDED. The validity lifetime, in seconds, of the token
issued by the authorization server. Oftentimes Oftentimes, the client will
not have the inclination or capability to inspect the content of
the token token, and this parameter provides a consistent and token-type-
agnostic token-
type-agnostic indication of how long the token can be expected to
be valid. For example, the value 1800 denotes that the token will
expire in thirty minutes from the time the response was generated.

scope
OPTIONAL,
OPTIONAL if the scope of the issued security token is identical to
the scope requested by the client; otherwise, it is REQUIRED.

refresh_token
OPTIONAL. A refresh token will typically not be issued when the
exchange is of one temporary credential (the subject_token) for a
different temporary credential (the issued token) for use in some
other context. A refresh token can be issued in cases where the
client of the token exchange needs the ability to access a
resource even when the original credential is no longer valid
(e.g., user-not-present or offline scenarios where there is no
longer any user entertaining an active session with the client).
Profiles or deployments of this specification should clearly
document the conditions under which a client should expect a
refresh token in response to "urn:ietf:params:oauth:grant-
type:token-exchange" grant type requests.

2.2.2. Error Response

If the request itself is not valid or if either the "subject_token"
or "actor_token" are invalid for any reason, or are unacceptable
based on policy, the authorization server MUST construct an error
response, as specified in Section 5.2 of [RFC6749]. The value of the
"error" parameter MUST be the "invalid_request" error code.

If the authorization server is unwilling or unable to issue a token
for any target service indicated by the "resource" or "audience"
parameters, the "invalid_target" error code SHOULD be used in the
error response.

The authorization server MAY include additional information regarding
the reasons for the error using the "error_description" as discussed
in Section 5.2 of [RFC6749].

Other error codes may also be used, as appropriate.

2.3. Example Token Exchange

The following example demonstrates a hypothetical token exchange in
which an OAuth resource server assumes the role of the client during
the exchange. It trades an access token, which it received in a
protected resource request, for a new token that it will use to call
to a backend service (extra line breaks and indentation in the
examples are for display purposes only).

Figure 1 shows the resource server receiving a protected resource
request containing an OAuth access token in the Authorization header,
as specified in Section 2.1 of [RFC6750].

GET /resource HTTP/1.1
Host: frontend.example.com
Authorization: Bearer accVkjcJyb4BWCxGsndESCJQbdFMogUC5PbRDqceLTC

Figure 1: Protected Resource Request

In Figure 2, the resource server assumes the role of client for the
token exchange exchange, and the access token from the request in Figure 1 is
sent to the authorization server using a request as specified in
Section 2.1. The value of the "subject_token" parameter carries the
access token token, and the value of the "subject_token_type" parameter
indicates that it is an OAuth 2.0 access token. The resource server,
acting in the role of the client, uses its identifier and secret to
authenticate to the authorization server using the HTTP Basic
authentication scheme. The "resource" parameter indicates the
location of the backend service, https://backend.example.com/api, <https://backend.example.com/api>,
where the issued token will be used.

POST /as/token.oauth2 HTTP/1.1
Host: as.example.com
Authorization: Basic cnMwODpsb25nLXNlY3VyZS1yYW5kb20tc2VjcmV0
Content-Type: application/x-www-form-urlencoded

grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange
&resource=https%3A%2F%2Fbackend.example.com%2Fapi
&subject_token=accVkjcJyb4BWCxGsndESCJQbdFMogUC5PbRDqceLTC
&subject_token_type=
urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aaccess_token

Figure 2: Token Exchange Request

The authorization server validates the client credentials and the
"subject_token" presented in the token exchange request. From the
"resource" parameter, the authorization server is able to determine
the appropriate policy to apply to the request and issues a token
suitable for use at https://backend.example.com. <https://backend.example.com>. The
"access_token" parameter of the response shown in Figure 3 contains
the new token, which is itself a bearer OAuth access token that is
valid for one minute. The token happens to be a JWT; however, its
structure and format are opaque to the client client, so the
"issued_token_type" indicates only that it is an access token.

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-cache, no-store

{
"access_token":"eyJhbGciOiJFUzI1NiIsImtpZCI6IjllciJ9.eyJhdWQiOiJo
dHRwczovL2JhY2tlbmQuZXhhbXBsZS5jb20iLCJpc3MiOiJodHRwczovL2FzLmV
4YW1wbGUuY29tIiwiZXhwIjoxNDQxOTE3NTkzLCJpYXQiOjE0NDE5MTc1MzMsIn
N1YiI6ImJkY0BleGFtcGxlLmNvbSIsInNjb3BlIjoiYXBpIn0.40y3ZgQedw6rx
f59WlwHDD9jryFOr0_Wh3CGozQBihNBhnXEQgU85AI9x3KmsPottVMLPIWvmDCM
y5-kdXjwhw",
"issued_token_type":
"urn:ietf:params:oauth:token-type:access_token",
"token_type":"Bearer",
"expires_in":60
}

Figure 3: Token Exchange Response

The resource server can then use the newly acquired access token in
making a request to the backend server as illustrated in Figure 4.

GET /api HTTP/1.1
Host: backend.example.com
Authorization: Bearer eyJhbGciOiJFUzI1NiIsImtpZCI6IjllciJ9.eyJhdWQ
iOiJodHRwczovL2JhY2tlbmQuZXhhbXBsZS5jb20iLCJpc3MiOiJodHRwczovL2
FzLmV4YW1wbGUuY29tIiwiZXhwIjoxNDQxOTE3NTkzLCJpYXQiOjE0NDE5MTc1M
zMsInN1YiI6ImJkY0BleGFtcGxlLmNvbSIsInNjb3BlIjoiYXBpIn0.40y3ZgQe
dw6rxf59WlwHDD9jryFOr0_Wh3CGozQBihNBhnXEQgU85AI9x3KmsPottVMLPIW
vmDCMy5-kdXjwhw

Figure 4: Backend Protected Resource Request

Additional examples can be found in Appendix A.

3. Token Type Identifiers

Several parameters in this specification utilize an identifier as the
value to describe the token in question. Specifically, they are the
"requested_token_type", "subject_token_type", and "actor_token_type"
parameters of the request and the "issued_token_type" member of the
response. Token type identifiers are URIs. Token Exchange exchange can work
with both tokens issued by other parties and tokens from the given
authorization server. For the former former, the token type identifier
indicates the syntax (e.g., JWT or SAML 2.0) so the authorization
server can parse it; for the latter latter, it indicates what the given
authorization server issued it for (e.g., access_token "access_token" or
refresh_token).
"refresh_token").

The following token type identifiers are defined by this
specification. Other URIs MAY be used to indicate other token types.

urn:ietf:params:oauth:token-type:access_token
Indicates that the token is an OAuth 2.0 access token issued by
the given authorization server.

urn:ietf:params:oauth:token-type:refresh_token
Indicates that the token is an OAuth 2.0 refresh token issued by
the given authorization server.

urn:ietf:params:oauth:token-type:id_token
Indicates that the token is an ID Token, Token as defined in Section 2 of
[OpenID.Core].

urn:ietf:params:oauth:token-type:saml1
Indicates that the token is a base64url-encoded SAML 1.1
[OASIS.saml-core-1.1] assertion.

urn:ietf:params:oauth:token-type:saml2
Indicates that the token is a base64url-encoded SAML 2.0
[OASIS.saml-core-2.0-os] assertion.

The value "urn:ietf:params:oauth:token-type:jwt", which is defined in
Section 9 of [JWT], indicates that the token is a JWT.

The distinction between an access token and a JWT is subtle. An
access token represents a delegated authorization decision, whereas
JWT is a token format. An access token can be formatted as a JWT but
doesn't necessarily have to be. And a JWT might well be an access
token
token, but not all JWTs are access tokens. The intent of this
specification is that "urn:ietf:params:oauth:token-type:access_token"
be an indicator that the token is a typical OAuth access token issued
by the authorization server in question, opaque to the client, and
usable the same manner as any other access token obtained from that
authorization server. (It could well be a JWT, but the client isn't
and needn't be aware of that fact.) Whereas,
"urn:ietf:params:oauth:token-type:jwt" is to indicate specifically
that a JWT is being requested or sent (perhaps in a cross-domain use- use
case where the JWT is used as an authorization grant to obtain an
access token from a different authorization server as is facilitated
by [RFC7523]).

Note that for tokens which that are binary in nature, the URI used for
conveying them needs to be associated with the semantics of a base64
or other encoding suitable for usage with HTTP and OAuth.

4. JSON Web Token Claims and Introspection Response Parameters

It is useful to have defined mechanisms to express delegation within
a token as well as to express authorization to delegate or
impersonate. Although the token exchange protocol described herein
can be used with any type of token, this section defines claims to
express such semantics specifically for JWTs and in an OAuth 2.0
Token Introspection [RFC7662] response. Similar definitions for
other types of tokens are possible but beyond the scope of this
specification.

Note that the claims not established herein but used in examples and
descriptions, such as "iss", "sub", "exp", etc., are defined by
[JWT].

4.1. "act" (Actor) Claim

The "act" (actor) claim provides a means within a JWT to express that
delegation has occurred and identify the acting party to whom
authority has been delegated. The "act" claim value is a JSON object
object, and members in the JSON object are claims that identify the
actor. The claims that make up the "act" claim identify and possibly
provide additional information about the actor. For example, the
combination of the two claims "iss" and "sub" might be necessary to
uniquely identify an actor.

However, claims within the "act" claim pertain only to the identity
of the actor and are not relevant to the validity of the containing
JWT in the same manner as the top-level claims. Consequently, non-
identity claims (e.g., "exp", "nbf", and "aud") are not meaningful
when used within an "act" claim, claim and therefore are therefore not used.

Figure 5 illustrates the "act" (actor) claim within a JWT Claims Set.
The claims of the token itself are about user@example.com while the
"act" claim indicates that admin@example.com is the current actor.

{
"aud":"https://consumer.example.com",
"iss":"https://issuer.example.com",
"exp":1443904177,
"nbf":1443904077,
"sub":"user@example.com",
"act":
{
"sub":"admin@example.com"
}
}

Figure 5: Actor Claim

A chain of delegation can be expressed by nesting one "act" claim
within another. The outermost "act" claim represents the current
actor while nested "act" claims represent prior actors. The least
recent actor is the most deeply nested. The nested "act" claims
serve as a history trail that connects the initial request and
subject through the various delegation steps undertaken before
reaching the current actor. In this sense, the current actor is
considered to include the entire authorization/delegation history,
leading naturally to the nested structure described here.

For the purpose of applying access control policy, the consumer of a
token MUST only consider the token's top-level claims and the party
identified as the current actor by the "act" claim. Prior actors
identified by any nested "act" claims are informational only and are
not to be considered in access control decisions.

The following example in Figure 6 illustrates nested "act" (actor)
claims within a JWT Claims Set. The claims of the token itself are
about user@example.com while the "act" claim indicates that the
system https://service16.example.com <https://service16.example.com> is the current actor and
https://service77.example.com
<https://service77.example.com> was a prior actor. Such a token
might come about as the result of service16 receiving a token in a
call from service77 and exchanging it for a token suitable to call
service26 while the authorization server notes the situation in the
newly issued token.

{
"aud":"https://service26.example.com",
"iss":"https://issuer.example.com",
"exp":1443904100,
"nbf":1443904000,
"sub":"user@example.com",
"act":
{
"sub":"https://service16.example.com",
"act":
{
"sub":"https://service77.example.com"
}
}
}

Figure 6: Nested Actor Claim

When included as a top-level member of an OAuth token introspection
response, "act" has the same semantics and format as the claim of the
same name.

4.2. "scope" (Scopes) Claim

The value of the "scope" claim is a JSON string containing a space-
separated list of scopes associated with the token, in the format
described in Section 3.3 of [RFC6749].

Figure 7 illustrates the "scope" claim within a JWT Claims Set.

{
"aud":"https://consumer.example.com",
"iss":"https://issuer.example.com",
"exp":1443904177,
"nbf":1443904077,
"sub":"dgaf4mvfs75Fci_FL3heQA",
"scope":"email profile phone address"
}

Figure 7: Scopes Claim

OAuth 2.0 Token Introspection [RFC7662] already defines the "scope"
parameter to convey the scopes associated with the token.

4.3. "client_id" (Client Identifier) Claim

The "client_id" claim carries the client identifier of the OAuth 2.0
[RFC6749] client that requested the token.

The following example in Figure 8 illustrates the "client_id" claim
within a JWT Claims Set indicating an OAuth 2.0 client with
"s6BhdRkqt3" as its identifier.

{
"aud":"https://consumer.example.com",
"iss":"https://issuer.example.com",
"exp":1443904177,
"sub":"user@example.com",
"client_id":"s6BhdRkqt3"
}

Figure 8: Client Identifier Claim

OAuth 2.0 Token Introspection [RFC7662] already defines the
"client_id" parameter as the client identifier for the OAuth 2.0
client that requested the token.

4.4. "may_act" (Authorized Actor) Claim

The "may_act" claim makes a statement that one party is authorized to
become the actor and act on behalf of another party. The claim might
be used, for example, when a "subject_token" is presented to the
token endpoint in a token exchange request and "may_act" claim in the
subject token can be used by the authorization server to determine
whether the client (or party identified in the "actor_token") is
authorized to engage in the requested delegation or impersonation.
The claim value is a JSON object object, and members in the JSON object are
claims that identify the party that is asserted as being eligible to
act for the party identified by the JWT containing the claim. The
claims that make up the "may_act" claim identify and possibly provide
additional information about the authorized actor. For example, the
combination of the two claims "iss" and "sub" are sometimes necessary
to uniquely identify an authorized actor, while the "email" claim
might be used to provide additional useful information about that
party.

However, claims within the "may_act" claim pertain only to the
identity of that party and are not relevant to the validity of the
containing JWT in the same manner as top-level claims. Consequently,
claims such as "exp", "nbf", and "aud" are not meaningful when used
within a "may_act" claim, claim and therefore are therefore not used.

Figure 9 illustrates the "may_act" claim within a JWT Claims Set.
The claims of the token itself are about user@example.com while the
"may_act" claim indicates that admin@example.com is authorized to act
on behalf of user@example.com.

{
"aud":"https://consumer.example.com",
"iss":"https://issuer.example.com",
"exp":1443904177,
"nbf":1443904077,
"sub":"user@example.com",
"may_act":
{
"sub":"admin@example.com"
}
}

Figure 9: Authorized Actor Claim

When included as a top-level member of an OAuth token introspection
response, "may_act" has the same semantics and format as the claim of
the same name.

5. Security Considerations

Much of the guidance from Section 10 of [RFC6749], the Security
Considerations in The OAuth 2.0 Authorization Framework, is also
applicable here. Furthermore, [RFC6819] provides additional security
considerations for OAuth OAuth, and [I-D.ietf-oauth-security-topics] [OAUTH-SECURITY] has updated security
guidance based on deployment experience and new threats that have
emerged since OAuth 2.0 was originally published.

All of the normal security issues that are discussed in [JWT],
especially in relationship to comparing URIs and dealing with
unrecognized values, also apply here.

In addition, both delegation and impersonation introduce unique
security issues. Any time one principal is delegated the rights of
another principal, the potential for abuse is a concern. The use of
the "scope" claim (in addition to other typical constraints such as a
limited token lifetime) is suggested to mitigate potential for such
abuse, as it restricts the contexts in which the delegated rights can
be exercised.

6. Privacy Considerations

Tokens employed in the context of the functionality described herein
may contain privacy-sensitive information and, to prevent disclosure
of such information to unintended parties, MUST only be transmitted
over encrypted channels, such as Transport Layer Security (TLS). In
cases where it is desirable to prevent disclosure of certain
information to the client, the token MUST be encrypted to its
intended recipient. Deployments SHOULD determine the minimally
necessary amount of data and only include such information in issued
tokens. In some cases, data minimization may include representing
only an anonymous or pseudonymous user.

7. IANA Considerations

7.1. OAuth URI Registration

This specification registers

IANA has registered the following values in the IANA "OAuth URI"
subregistry of the "OAuth Parameters" registry [IANA.OAuth.Parameters]
[IANA.OAuth.Parameters]. The "OAuth URI" subregistry was established
by [RFC6755].

7.1.1. Registry Contents

* URN: urn:ietf:params:oauth:grant-type:token-exchange
o
* Common Name: Token exchange grant type for OAuth 2.0
o
* Change controller: Controller: IESG
o
* Specification Document: Section 2.1 of [[ this specification ]]

o RFC 8693

* URN: urn:ietf:params:oauth:token-type:access_token
o
* Common Name: Token type URI for an OAuth 2.0 access token
o
* Change controller: Controller: IESG
o
* Specification Document: Section 3 of [[this specification]]

o RFC 8693

* URN: urn:ietf:params:oauth:token-type:refresh_token
o
* Common Name: Token type URI for an OAuth 2.0 refresh token
o
* Change controller: Controller: IESG
o
* Specification Document: Section 3 of [[this specification]]
o RFC 8693

* URN: urn:ietf:params:oauth:token-type:id_token
o
* Common Name: Token type URI for an ID Token
o
* Change controller: Controller: IESG
o
* Specification Document: Section 3 of [[this specification]]

o RFC 8693

* URN: urn:ietf:params:oauth:token-type:saml1
o
* Common Name: Token type URI for a base64url-encoded SAML 1.1
assertion
o
* Change Controller: IESG
o
* Specification Document: Section 3 of [[this specification]]

o RFC 8693

* URN: urn:ietf:params:oauth:token-type:saml2
o
* Common Name: Token type URI for a base64url-encoded SAML 2.0
assertion
o
* Change Controller: IESG
o
* Specification Document: Section 3 of [[this specification]] RFC 8693

7.2. OAuth Parameters Registration

This specification registers

IANA has registered the following values in the IANA "OAuth Parameters"
subregistry of the "OAuth Parameters" registry [IANA.OAuth.Parameters]
[IANA.OAuth.Parameters]. The "OAuth Parameters" subregistry was
established by [RFC6749].

7.2.1. Registry Contents

o Parameter name: resource
o Parameter usage location: token request
o Change controller: IESG
o Specification document(s): Section 2.1 of [[ this specification ]]

* Parameter name: audience
o
* Parameter usage location: token request
o
* Change controller: IESG
o
* Specification document(s): Section 2.1 of [[ this specification ]]

o RFC 8693

* Parameter name: requested_token_type
o
* Parameter usage location: token request
o
* Change controller: IESG
o
* Specification document(s): Section 2.1 of [[ this specification ]]

o RFC 8693

* Parameter name: subject_token
o
* Parameter usage location: token request
o
* Change controller: IESG
o
* Specification document(s): Section 2.1 of [[ this specification ]]

o RFC 8693

* Parameter name: subject_token_type
o
* Parameter usage location: token request
o
* Change controller: IESG
o
* Specification document(s): Section 2.1 of [[ this specification ]]

o RFC 8693

* Parameter name: actor_token
o
* Parameter usage location: token request
o
* Change controller: IESG
o
* Specification document(s): Section 2.1 of [[ this specification ]]

o RFC 8693

* Parameter name: actor_token_type
o
* Parameter usage location: token request
o
* Change controller: IESG
o
* Specification document(s): Section 2.1 of [[ this specification ]]

o RFC 8693

* Parameter name: issued_token_type
o
* Parameter usage location: token response
o
* Change controller: IESG
o
* Specification document(s): Section 2.2.1 of [[ this specification
]] RFC 8693

7.3. OAuth Access Token Type Registration

This specification registers

IANA has registered the following access token type in the
IANA "OAuth
Access Token Types" subregistry of the "OAuth Parameters" registry [IANA.OAuth.Parameters]
[IANA.OAuth.Parameters]. The "OAuth Access Token Types" subregistry
was established by [RFC6749].

7.3.1. Registry Contents

* Type name: N_A
o
* Additional Token Endpoint Response Parameters: (none)
o none
* HTTP Authentication Scheme(s): (none)
o none
* Change controller: IESG
o
* Specification document(s): Section 2.2.1 of [[ this specification
]] RFC 8693

7.4. JSON Web Token Claims Registration

This specification registers

IANA has registered the following Claims in the IANA "JSON Web Token
Claims" subregistry of the "JSON Web Token (JWT)" registry [IANA.JWT.Claims]
[IANA.JWT]. The "JSON Web Token Claims" subregistry was established
by [JWT].

7.4.1. Registry Contents

* Claim Name: "act"
o act
* Claim Description: Actor
o
* Change Controller: IESG
o
* Specification Document(s): Section 4.1 of [[ this specification ]]

o RFC 8693

* Claim Name: "scope"
o scope
* Claim Description: Scope Values
o
* Change Controller: IESG
o
* Specification Document(s): Section 4.2 of [[ this specification ]]

o RFC 8693

* Claim Name: "client_id"
o client_id
* Claim Description: Client Identifier
o
* Change Controller: IESG
o
* Specification Document(s): Section 4.3 of [[ this specification ]]

o RFC 8693

* Claim Name: "may_act"
o may_act
* Claim Description: Authorized Actor - the party that is authorized
to become the actor
o
* Change Controller: IESG
o
* Specification Document(s): Section 4.4 of [[ this specification ]] RFC 8693

7.5. OAuth Token Introspection Response Registration

This specification registers

IANA has registered the following values in the IANA "OAuth Token
Introspection Response" registry [IANA.OAuth.Parameters] of the "OAuth Parameters" registry
[IANA.OAuth.Parameters]. The "OAuth Token Introspection Response"
registry was established by [RFC7662].

7.5.1. Registry Contents

o Claim

* Name: "act"
o Claim act
* Description: Actor
o
* Change Controller: IESG
o
* Specification Document(s): Section 4.1 of [[ this specification ]]

o Claim RFC 8693

* Name: "may_act"
o Claim may_act
* Description: Authorized Actor - the party that is authorized to
become the actor
o
* Change Controller: IESG
o
* Specification Document(s): Section 4.4 of [[ this specification ]]

7.6. OAuth Extensions Error Registration

This specification registers the following values in the IANA "OAuth
Extensions Error" registry [IANA.OAuth.Parameters] established by
[RFC6749].

7.6.1. Registry Contents

o Error Name: "invalid_target"
o Error Usage Location: token error response
o Related Protocol Extension: OAuth 2.0 Token Exchange
o Change Controller: IETF
o Specification Document(s): Section 2.2.2 of [[ this specification
]] RFC 8693

8. References

8.1. Normative References

[IANA.JWT.Claims]

[IANA.JWT] IANA, "JSON Web Token Claims",
<http://www.iana.org/assignments/jwt>. (JWT)",
<https://www.iana.org/assignments/jwt>.

[IANA.OAuth.Parameters]
IANA, "OAuth Parameters",
<http://www.iana.org/assignments/oauth-parameters>.
<https://www.iana.org/assignments/oauth-parameters>.

[JWT] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<http://tools.ietf.org/html/rfc7519>.
<https://www.rfc-editor.org/info/rfc7519>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.

[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.

[RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7662, DOI 10.17487/RFC7662, October 2015,
<https://www.rfc-editor.org/info/rfc7662>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.

8.2. Informative References
[I-D.ietf-oauth-resource-indicators]
Campbell, B., Bradley, J., and H. Tschofenig, "Resource
Indicators for OAuth 2.0", draft-ietf-oauth-resource-
indicators-02 (work in progress), January 2019.

[I-D.ietf-oauth-security-topics]
Lodderstedt, T., Bradley, J., Labunets, A., and D. Fett,
"OAuth 2.0 Security Best Current Practice", draft-ietf-
oauth-security-topics-13 (work in progress), July 2019.

[OASIS.saml-core-1.1]
Maler, E., Mishra, P., and R. Philpott, "Assertions and
Protocol for the OASIS Security Assertion Markup Language
(SAML) V1.1", OASIS Standard oasis-sstc-saml-core-1.1,
September 2003. 2003, <https://www.oasis-
open.org/committees/download.php/3406/oasis-sstc-saml-
core-1.1.pdf>.

[OASIS.saml-core-2.0-os]
Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005. 2005, <http://docs.oasis-
open.org/security/saml/v2.0/saml-core-2.0-os.pdf>.

[OAUTH-RESOURCE]
Campbell, B., Bradley, J., and H. Tschofenig, "Resource
Indicators for OAuth 2.0", Work in Progress, Internet-
Draft, draft-ietf-oauth-resource-indicators-08, 11
September 2019, <https://tools.ietf.org/html/draft-ietf-
oauth-resource-indicators-08>.

[OAUTH-SECURITY]
Lodderstedt, T., Bradley, J., Labunets, A., and D. Fett,
"OAuth 2.0 Security Best Current Practice", Work in
Progress, Internet-Draft, draft-ietf-oauth-security-
topics-13, 8 July 2019, <https://tools.ietf.org/html/
draft-ietf-oauth-security-topics-13>.

[OpenID.Core]
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0", November 2014,
<http://openid.net/specs/openid-connect-core-1_0.html>.
<https://openid.net/specs/openid-connect-core-1_0.html>.

[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<https://www.rfc-editor.org/info/rfc6750>.

[RFC6755] Campbell, B. and H. Tschofenig, "An IETF URN Sub-Namespace
for OAuth", RFC 6755, DOI 10.17487/RFC6755, October 2012,
<https://www.rfc-editor.org/info/rfc6755>.

[RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0
Threat Model and Security Considerations", RFC 6819,
DOI 10.17487/RFC6819, January 2013,
<https://www.rfc-editor.org/info/rfc6819>.

[RFC7521] Campbell, B., Mortimore, C., Jones, M., and Y. Goland,
"Assertion Framework for OAuth 2.0 Client Authentication
and Authorization Grants", RFC 7521, DOI 10.17487/RFC7521,
May 2015, <https://www.rfc-editor.org/info/rfc7521>.

[RFC7523] Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token
(JWT) Profile for OAuth 2.0 Client Authentication and
Authorization Grants", RFC 7523, DOI 10.17487/RFC7523, May
2015, <https://www.rfc-editor.org/info/rfc7523>.

[WS-Trust] Nadalin, A., Ed., Goodner, M., Ed., Gudgin, M., Ed.,
Barbir, A., Ed., and H. Granqvist, Ed., "WS-Trust 1.4",
February 2012,
<http://docs.oasis-open.org/ws-sx/ws-trust/v1.4/
ws-trust.html>. <https://docs.oasis-open.org/ws-sx/ws-
trust/v1.4/ws-trust.html>.

Appendix A. Additional Token Exchange Examples

Two example token exchanges are provided in the following sections
illustrating impersonation and delegation, respectively (with extra
line breaks and indentation for display purposes only).

A.1. Impersonation Token Exchange Example

A.1.1. Token Exchange Request

In the following token exchange request, a client is requesting a
token with impersonation semantics (with (delegation is impossible with
only a "subject_token" and no "actor_token", delegation is impossible). "actor_token"). The client tells the
authorization server that it needs a token for use at the target
service with the logical name "urn:example:cooperation-context".

POST /as/token.oauth2 HTTP/1.1
Host: as.example.com
Content-Type: application/x-www-form-urlencoded

Figure 10: Token Exchange Request

A.1.2. Subject Token Claims

The "subject_token" in the prior request is a JWT JWT, and the decoded
JWT Claims Set is shown here. The JWT is intended for consumption by
the authorization server within a specific time window. The subject
of the JWT ("bdc@example.net") is the party on behalf of whom the new
token is being requested.

{
"aud":"https://as.example.com",
"iss":"https://original-issuer.example.net",
"exp":1441910600,
"nbf":1441909000,
"sub":"bdc@example.net",
"scope":"orders profile history"
}

Figure 11: Subject Token Claims

A.1.3. Token Exchange Response

The "access_token" parameter of the token exchange response shown
below contains the new token that the client requested. The other
parameters of the response indicate that the token is a bearer access
token that expires in an hour.

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-cache, no-store

{
"access_token":"eyJhbGciOiJFUzI1NiIsImtpZCI6IjcyIn0.eyJhdWQiOiJ1cm4
6ZXhhbXBsZTpjb29wZXJhdGlvbi1jb250ZXh0IiwiaXNzIjoiaHR0cHM6Ly9hcy5l
eGFtcGxlLmNvbSIsImV4cCI6MTQ0MTkxMzYxMCwic3ViIjoiYmRjQGV4YW1wbGUub
mV0Iiwic2NvcGUiOiJvcmRlcnMgcHJvZmlsZSBoaXN0b3J5In0.rMdWpSGNACTvnF
uOL74sYZ6MVuld2Z2WkGLmQeR9ztj6w2OXraQlkJmGjyiCq24kcB7AI2VqVxl3wSW
nVKh85A",
"issued_token_type":
"urn:ietf:params:oauth:token-type:access_token",
"token_type":"Bearer",
"expires_in":3600
}

Figure 12: Token Exchange Response

A.1.4. Issued Token Claims

The decoded JWT Claims Set of the issued token is shown below. The
new JWT is issued by the authorization server and intended for
consumption by a system entity known by the logical name
"urn:example:cooperation-context" any time before its expiration.
The subject ("sub") of the JWT is the same as the subject the token
used to make the request, which effectively enables the client to
impersonate that subject at the system entity known by the logical
name of "urn:example:cooperation-context" by using the token.

{
"aud":"urn:example:cooperation-context",
"iss":"https://as.example.com",
"exp":1441913610,
"sub":"bdc@example.net",
"scope":"orders profile history"
}

Figure 13: Issued Token Claims

A.2. Delegation Token Exchange Example

A.2.1. Token Exchange Request

In the following token exchange request, a client is requesting a
token and providing both a "subject_token" and an "actor_token". The
client tells the authorization server that it needs a token for use
at the target service with the logical name "urn:example:cooperation-
context". Policy at the authorization server dictates that the
issued token be a composite.

POST /as/token.oauth2 HTTP/1.1
Host: as.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange
&audience=urn%3Aexample%3Acooperation-context
&subject_token=eyJhbGciOiJFUzI1NiIsImtpZCI6IjE2In0.eyJhdWQiOiJodHRwc
zovL2FzLmV4YW1wbGUuY29tIiwiaXNzIjoiaHR0cHM6Ly9vcmlnaW5hbC1pc3N1ZXI
uZXhhbXBsZS5uZXQiLCJleHAiOjE0NDE5MTAwNjAsInNjb3BlIjoic3RhdHVzIGZlZ
WQiLCJzdWIiOiJ1c2VyQGV4YW1wbGUubmV0IiwibWF5X2FjdCI6eyJzdWIiOiJhZG1
pbkBleGFtcGxlLm5ldCJ9fQ.4rPRSWihQbpMIgAmAoqaJojAxj-p2X8_fAtAGTXrvM
xU-eEZHnXqY0_AOZgLdxw5DyLzua8H_I10MCcckF-Q_g
&subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Ajwt
&actor_token=eyJhbGciOiJFUzI1NiIsImtpZCI6IjE2In0.eyJhdWQiOiJodHRwczo
vL2FzLmV4YW1wbGUuY29tIiwiaXNzIjoiaHR0cHM6Ly9vcmlnaW5hbC1pc3N1ZXIuZ
XhhbXBsZS5uZXQiLCJleHAiOjE0NDE5MTAwNjAsInN1YiI6ImFkbWluQGV4YW1wbGU
ubmV0In0.7YQ-3zPfhUvzje5oqw8COCvN5uP6NsKik9CVV6cAOf4QKgM-tKfiOwcgZ
oUuDL2tEs6tqPlcBlMjiSzEjm3yBg
&actor_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Ajwt

Figure 14: Token Exchange Request

A.2.2. Subject Token Claims

The "subject_token" in the prior request is a JWT JWT, and the decoded
JWT Claims Set is shown here. The JWT is intended for consumption by
the authorization server before a specific expiration time. The
subject of the JWT ("user@example.net") is the party on behalf of
whom the new token is being requested.

{
"aud":"https://as.example.com",
"iss":"https://original-issuer.example.net",
"exp":1441910060,
"scope":"status feed",
"sub":"user@example.net",
"may_act":
{
"sub":"admin@example.net"
}
}

Figure 15: Subject Token Claims

A.2.3. Actor Token Claims

The "actor_token" in the prior request is a JWT JWT, and the decoded JWT
Claims Set is shown here. This JWT is also intended for consumption
by the authorization server before a specific expiration time. The
subject of the JWT ("admin@example.net") is the actor that will wield
the security token being requested.

{
"aud":"https://as.example.com",
"iss":"https://original-issuer.example.net",
"exp":1441910060,
"sub":"admin@example.net"
}

Figure 16: Actor Token Claims

A.2.4. Token Exchange Response

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-cache, no-store

{
"access_token":"eyJhbGciOiJFUzI1NiIsImtpZCI6IjcyIn0.eyJhdWQiOiJ1cm4
6ZXhhbXBsZTpjb29wZXJhdGlvbi1jb250ZXh0IiwiaXNzIjoiaHR0cHM6Ly9hcy5l
eGFtcGxlLmNvbSIsImV4cCI6MTQ0MTkxMzYxMCwic2NvcGUiOiJzdGF0dXMgZmVlZ
CIsInN1YiI6InVzZXJAZXhhbXBsZS5uZXQiLCJhY3QiOnsic3ViIjoiYWRtaW5AZX
hhbXBsZS5uZXQifX0.3paKl9UySKYB5ng6_cUtQ2qlO8Rc_y7Mea7IwEXTcYbNdwG
9-G1EKCFe5fW3H0hwX-MSZ49Wpcb1SiAZaOQBtw",
"issued_token_type":"urn:ietf:params:oauth:token-type:jwt",
"token_type":"N_A",
"expires_in":3600
}

Figure 17: Token Exchange Response

A.2.5. Issued Token Claims

The decoded JWT Claims Set of the issued token is shown below. The
new JWT is issued by the authorization server and intended for
consumption by a system entity known by the logical name
"urn:example:cooperation-context" any time before its expiration.
The subject ("sub") of the JWT is the same as the subject of the
"subject_token" used to make the request. The actor ("act") of the
JWT is the same as the subject of the "actor_token" used to make the
request. This indicates delegation and identifies
"admin@example.net" as the current actor to whom authority has been
delegated to act on behalf of "user@example.net".

{
"aud":"urn:example:cooperation-context",
"iss":"https://as.example.com",
"exp":1441913610,
"scope":"status feed",
"sub":"user@example.net",
"act":
{
"sub":"admin@example.net"
}
}

Figure 18: Issued Token Claims

Appendix B.

Acknowledgements

This specification was developed within the OAuth Working Group,
which includes dozens of active and dedicated participants. It was
produced under the chairmanship of Hannes Tschofenig, Derek Atkins,
and Rifaat Shekh-Yusef Shekh-Yusef, with Kathleen Moriarty, Stephen Farrell, Eric
Rescorla, Roman Danyliw, and Benjamin Kaduk serving as Security Area
Directors.

The following individuals contributed ideas, feedback, and wording to
this specification: Caleb Baker, Vittorio Bertocci, Mike Brown,
Thomas Broyer, Roman Danyliw, William Denniss, Vladimir Dzhuvinov,
Eric Fazendin, Phil Hunt, Benjamin Kaduk, Jason Keglovitz, Torsten
Lodderstedt, Barry Leiba, Adam Lewis, James Manger, Nov Matake, Matt
Miller, Hilarie Orman, Matthew Perry, Eric Rescorla, Justin Richer,
Adam Roach, Rifaat Shekh-Yusef, Scott Tomilson, and Hannes
Tschofenig.

Appendix C. Document History

[[ to be removed by the RFC Editor before publication as an RFC ]]

-19

o Fix-up changes introduced in -18.
o Fix invalid JSON in the Nested Actor Claim example.
o Reference figure numbers in text when introducing the examples in
Section 2 and 4.
o Editorial updates from additional IESG evaluation comments.
o Add an informational reference to ietf-oauth-resource-indicators
o Update ietf-oauth-security-topics ref to 13

-18

o Editorial updates based on a few more IESG evaluation comments.

-17

o Editorial improvements and example fixes resulting from IESG
evaluation comments.
o Added a pointer to RFC6749's Appendix B. on the "Use of
application/x-www-form-urlencoded Media Type" as a way of
providing a normative citation (by reference) for the media type.
o Strengthened some of the wording in the privacy considerations to
bring it inline with RFC 7519 Sec. 12 and RFC 6749 Sec. 10.8.

-16

o Fixed typo and added an AD to Acknowledgements.

-15

o Updated the nested actor claim example to (hopefully) be more
straightforward.
o Reworked Privacy Considerations to say to use TLS in transit,
minimize the amount of information in the token, and encrypt the
token if disclosure of its information to the client is a concern
per https://mailarchive.ietf.org/arch/msg/secdir/
KJhx4aq_U5uk3k6zpYP-CEHbpVM
o Moved the Security and Privacy Considerations sections to before
the IANA Considerations.

-14

o Added text in Section 4.1 about the "act" claim stating that only
the top-level claims and the current actor are to be considered in
applying access control decisions.

-13

o Updated the claim name and value syntax for scope to be consistent
with the treatment of scope in RFC 7662 OAuth 2.0 Token
Introspection.
o Updated the client identifier claim name to be consistent with the
treatment of client id in RFC 7662 OAuth 2.0 Token Introspection.

-12

o Updated to use the boilerplate from RFC 8174.

-11

o Added new WG chair and AD to the Acknowledgements.
o Applied clarifications suggested during AD review by EKR.

-10

o Defined token type URIs for base64url-encoded SAML 1.1 and SAML
2.0 assertions.
o Applied editorial fixes.

-09

o Changed "security tokens obtained could be used in a number of
contexts" to "security tokens obtained may be used in a number of
contexts" per a WGLC suggestion.

o Clarified that the validity of the subject or actor token have no
impact on the validity of the issued token after the exchange has
occurred per a WGLC comment.
o Changed use of invalid_target error code to a SHOULD per a WGLC
comment.
o Clarified text about non-identity claims within the "act" claim
being meaningless per a WGLC comment.
o Added brief Privacy Considerations section per WGLC comments.

-08

o Use the bibxml reference for OpenID.Core rather than defining it
inline.
o Added editor role for Campbell.
o Minor clarification of the text for actor_token.

-07

o Fixed typo (desecration -> discretion).
o Added an explanation of the relationship between scope, audience
and resource in the request and added an "invalid_target" error
code enabling the AS to tell the client that the requested
audiences/resources were too broad.

-06

o Drop "An STS for the REST of Us" from the title.
o Drop "heavyweight" and "lightweight" from the abstract and
introduction.
o Clarifications on the language around xxxxxx_token_type.
o Remove the want_composite parameter.
o Add a short mention of proof-of-possession style tokens to the
introduction and remove the respective open issue.

-05

o Defined the JWT claim "cid" to express the OAuth 2.0 client
identifier of the client that requested the token.
o Defined and requested registration for "act" and "may_act" as
Token introspection response parameters (in addition to being JWT
claims).
o Loosen up the language about refresh_token in the response to
OPTIONAL from NOT RECOMMENDED based on feedback form real world
deployment experience.
o Add clarifying text about the distinction between JWT and access
token URIs.
o Close out (remove) some of the Open Issues bullets that have been
resolved.

-04

o Clarified that the "resource" and "audience" request parameters
can be used at the same time (via http://www.ietf.org/mail-
archive/web/oauth/current/msg15335.html).
o Clarified subject/actor token validity after token exchange and
explained a bit more about the recommendation to not issue refresh
tokens (via http://www.ietf.org/mail-archive/web/oauth/current/
msg15318.html).
o Updated the examples appendix to use an issuer value that doesn't
imply that the client issued and signed the tokens and used
"Bearer" and "urn:ietf:params:oauth:token-type:access_token" in
one of the responses (via http://www.ietf.org/mail-
archive/web/oauth/current/msg15335.html).
o Defined and registered urn:ietf:params:oauth:token-type:id_token,
since some use cases perform token exchanges for ID Tokens and no
URI to indicate that a token is an ID Token had previously been
defined.

-03

o Updated the document editors (adding Campbell, Bradley, and
Mortimore).
o Added to the title.
o Added to the abstract and introduction.
o Updated the format of the request to use application/x-www-form-
urlencoded request parameters and the response to use the existing
token endpoint JSON parameters defined in OAuth 2.0.
o Changed the grant type identifier to urn:ietf:params:oauth:grant-
type:token-exchange.
o Added RFC 6755 registration requests for
urn:ietf:params:oauth:token-type:refresh_token,
urn:ietf:params:oauth:token-type:access_token, and
urn:ietf:params:oauth:grant-type:token-exchange.
o Added RFC 6749 registration requests for request/response
parameters.
o Removed the Implementation Considerations and the requirement to
support JWTs.
o Clarified many aspects of the text.
o Changed "on_behalf_of" to "subject_token",
"on_behalf_of_token_type" to "subject_token_type", "act_as" to
"actor_token", and "act_as_token_type" to "actor_token_type".
o Added an "audience" request parameter used to indicate the logical
names of the target services at which the client intends to use
the requested security token.
o Added a "want_composite" request parameter used to indicate the
desire for a composite token rather than trying to infer it from
the presence/absence of token(s) in the request.

o Added a "resource" request parameter used to indicate the URLs of
resources at which the client intends to use the requested
security token.
o Specified that multiple "audience" and "resource" request
parameter values may be used.
o Defined the JWT claim "act" (actor) to express the current actor
or delegation principal.
o Defined the JWT claim "may_act" to express that one party is
authorized to act on behalf of another party.
o Defined the JWT claim "scp" (scopes) to express OAuth 2.0 scope-
token values.
o Added the "N_A" (not applicable) OAuth Access Token Type
definition for use in contexts in which the token exchange syntax
requires a "token_type" value, but in which the token being issued
is not an access token.
o Added examples.

-02

o Enabled use of Security Token types other than JWTs for "act_as"
and "on_behalf_of" request values.
o Referenced the JWT and OAuth Assertions RFCs.

-01

o Updated references.

-00

o Created initial working group draft from draft-jones-oauth-token-
exchange-01.

Authors' Addresses

Michael B. Jones
Microsoft

Email: mbj@microsoft.com
URI: http://self-issued.info/ https://self-issued.info/

Anthony Nadalin
Microsoft

Email: tonynad@microsoft.com

Brian Campbell (editor)
Ping Identity

Email: brian.d.campbell@gmail.com

John Bradley
Yubico

Email: ve7jtb@ve7jtb.com

Chuck Mortimore
Salesforce
Visa

Email: cmortimore@salesforce.com chuck.mortimore@visa.com