OAuth Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track J. Bradley
Expires: March 24, 2017 B. Campbell
Ping Identity
September 20, 2016
OAuth 2.0 Token Binding
draft-ietf-oauth-token-binding-01
Abstract
This specification enables OAuth 2.0 implementations to apply Token
Binding to Access Tokens and Refresh Tokens. This cryptographically
binds these tokens to the TLS connections over which they are
intended to be used. This use of Token Binding protects these tokens
from man-in-the-middle and token export and replay attacks.
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on March 24, 2017.
Copyright Notice
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document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Notation and Conventions . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Token Binding for Refresh Tokens . . . . . . . . . . . . . . 3
3. Token Binding for Access Tokens . . . . . . . . . . . . . . . 4
3.1. Access Tokens Issued from the Authorization Endpoint . . 5
3.2. Access Tokens Issued from the Token Endpoint . . . . . . 5
3.3. Protected Resource Token Binding Validation . . . . . . . 5
3.4. Representing Token Binding in JWT Access Tokens . . . . . 5
4. Phasing in Token Binding and Preventing Downgrade Attacks . . 6
5. Token Binding Metadata . . . . . . . . . . . . . . . . . . . 7
5.1. Token Binding Client Metadata . . . . . . . . . . . . . . 7
5.2. Token Binding Authorization Server Metadata . . . . . . . 7
5.3. Token Binding Protected Resource Metadata . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7.1. OAuth Dynamic Client Registration Metadata Registration . 8
7.1.1. Registry Contents . . . . . . . . . . . . . . . . . . 8
7.2. OAuth Authorization Server Metadata Registration . . . . 8
7.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 9
7.3. OAuth Protected Resource Metadata Registration . . . . . 9
7.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 11
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . 11
Appendix C. Document History . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
This specification enables OAuth 2.0 [RFC6749] implementations to
apply Token Binding The Token Binding Protocol Version 1.0
[I-D.ietf-tokbind-protocol] Token Binding over HTTP
[I-D.ietf-tokbind-https] to Access Tokens and Refresh Tokens. This
cryptographically binds these tokens to the TLS connections over
which they are intended to be used. This use of Token Binding
protects these tokens from man-in-the-middle and token export and
replay attacks.
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1.1. 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 RFC
2119 [RFC2119].
1.2. Terminology
This specification uses the terms "Access Token", "Authorization
Endpoint", "Authorization Server", "Client", "Protected Resource",
"Refresh Token", and "Token Endpoint" defined by OAuth 2.0 [RFC6749],
the terms "Claim" and "JSON Web Token (JWT)" defined by JSON Web
Token (JWT) [JWT], the term "User Agent" defined by RFC 7230
[RFC7230], and the terms "Provided", "Referred", "Token Binding" and
"Token Binding ID" defined by Token Binding over HTTP
[I-D.ietf-tokbind-https].
2. Token Binding for Refresh Tokens
Token Binding of refresh tokens is a straightforward first-party
scenario, applying term "first-party" as used in Token Binding over
HTTP [I-D.ietf-tokbind-https]. It cryptographically binds the
refresh token to the TLS connection between the client and the token
endpoint. This case is straightforward because the refresh token is
both retrieved by the client from the token endpoint and sent by the
client to the token endpoint. Unlike the federated scenarios
described in Section 4 (Federation Use Cases) of Token Binding over
HTTP [I-D.ietf-tokbind-https] and the access token case described in
the next section, only a single TLS connection is involved in the
refresh token case.
Token Binding a refresh token requires that the authorization server
do two things. First, when refresh token is sent to the client, the
authorization server needs to remember the Provided Token Binding ID
and remember its association with the issued refresh token. Second,
when a token request containing a refresh token is received at the
token endpoint, the authorization server needs to verify that the
Provided Token Binding ID for the request matches the remembered
Token Binding ID associated with the refresh token. If the Token
Binding IDs do not match, the authorization server should return an
error in response to the request.
How the authorization server remembers the association between the
refresh token and the Token Binding ID is an implementation detail
that beyond the scope of this specification. Some authorization
servers will choose to store the Token Binding ID (or a cryptographic
hash of it, such a SHA-256 hash [SHS]) in the refresh token itself,
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thus reducing the amount of state to be kept by the server. Other
authorization servers will add the Token Binding ID value (or a hash
of it) to an internal data structure also containing other
information about the refresh token, such as grant type information.
These choices make no difference to the client, since the refresh
token is opaque to it.
3. Token Binding for Access Tokens
Token Binding for access tokens cryptographically binds the access
token to the TLS connection between the client and the protected
resource. Token Binding is applied to access tokens in a similar
manner to that described in Section 4 (Federation Use Cases) of Token
Binding over HTTP [I-D.ietf-tokbind-https]. It also builds upon the
mechanisms for Token Binding of ID Tokens defined in OpenID Connect
Token Bound Authentication 1.0 [OpenID.TokenBinding].
In the OpenID Connect [OpenID.Core] use case, HTTP redirects are used
to pass information between the identity provider and the relying
party; this HTTP redirect makes the Token Binding ID of the relying
party available to the identity provider as the Referred Token
Binding ID, information about which is then added to the ID Token.
No such redirect occurs between the authorization server and the
protected resource in the access token case; therefore, information
about the Token Binding ID for the TLS connection between the client
and the protected resource needs to be explicitly communicated by the
client to the authorization server to achieve Token Binding of the
access token.
This information is passed to the authorization server using the
Referred Token Binding ID, just as in the ID Token case. The only
difference is that the client needs to explicitly communicate the
Token Binding ID of the TLS connection between the client and the
protected resource to the Token Binding implementation so that it is
sent as the Referred Token Binding ID in the request to the
authorization server. This functionality provided by Token Binding
implementations is described in Section 5 (Implementation
Considerations) of Token Binding over HTTP [I-D.ietf-tokbind-https].
Note that to obtain this Token Binding ID, the client may need to
establish a TLS connection between itself and the protected resource
prior to making the request to the authorization server so that the
Provided Token Binding ID for the TLS connection to the protected
resource can be obtained. How the client retrieves this Token
Binding ID from the underlying Token Binding API is implementation
and operating system specific. An alternative, if supported, is for
the client to generate a Token Binding key to use for the protected
resource, use the Token Binding ID for that key, and then later use
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that key when the TLS connection to the protected resource is
established.
3.1. Access Tokens Issued from the Authorization Endpoint
For access tokens returned directly from the authorization endpoint,
such as with the implicit grant defined in Section 4.2 of OAuth 2.0
[RFC6749], the Referred Token Binding ID used to bind the access
token is sent with the authorization request. Upon receiving the
Referred Token Binding ID in an authorization request, the
authorization server then records it (or a cryptographic hash of it)
in the issued access token. Alternatively, in some implementations,
the resource's Token Binding ID information might be communicated to
the protected resource by other means, such as by introspecting
[RFC7662] the access token.
3.2. Access Tokens Issued from the Token Endpoint
For access tokens returned from the token endpoint, the Referred
Token Binding ID used to bind the access token is sent with the token
request. This applies to all the conventional grant types from OAuth
2.0 [RFC6749], including but not limited to refresh and authorization
code token requests, as well as extension grants, such as JWT
assertion authorization grants [RFC7523]. In this case, the Token
Binding ID of the TLS connection between the client and the protected
resource is sent to the authorization server at the token endpoint as
the Referred Token Binding ID. The authorization server then records
it (or a cryptographic hash of it) in the issued access token or
communicates it to the protected resource by other means, just as in
the previous case.
3.3. Protected Resource Token Binding Validation
Upon receiving a token bound access token, the protected resource
validates the binding by comparing the Provided Token Binding ID to
the Token Binding ID for the access token. Alternatively,
cryptographic hashes of these Token Binding ID values can be
compared. If the values do not match, the resource access attempt
MUST be rejected with an error.
3.4. Representing Token Binding in JWT Access Tokens
If the access token is represented as a JWT, the token binding
information SHOULD be represented in the same way that it is in token
bound OpenID Connect ID Tokens [OpenID.TokenBinding]. That
specification defines the new JWT Confirmation Method RFC 7800
[RFC7800] member "tbh" (token binding hash) to represent the SHA-256
hash of a Token Binding ID in an ID Token. The value of the "tbh"
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member is the base64url encoding of the SHA-256 hash of the Token
Binding ID.
The following example demonstrates the JWT Claims Set of an access
token containing the base64url encoding of the SHA-256 hash of a
Token Binding ID as the value of the "tbh" (token binding hash)
element in the "cnf" (confirmation) claim:
{
"iss": "https://server.example.com",
"aud": "https://resource.example.com",
"iat": 1467324320,
"exp": 1467324920,
"cnf":{
"tbh": "n0jI3trBK6_Gp2qiLOf48ZEZTjpBnhm-QOyzJxhBeAk"
}
}
4. Phasing in Token Binding and Preventing Downgrade Attacks
Many OAuth implementations will be deployed in situations in which
not all participants support Token Binding. Any of combination of
the client, the authorization server, the protected resource, and the
user agent may not yet support Token Binding, in which case it will
not work end-to-end.
It is a context-dependent deployment choice whether to allow
interactions to proceed in which Token Binding is not supported or
whether to treat Token Binding failures at any step as fatal errors.
Particularly in dynamic deployment environments in which End Users
have choices of clients, authorization servers, protected resources,
and/or user agents, it is RECOMMENDED that authorizations using one
or more components that do not implement Token Binding be allowed to
successfully proceed. This enables different components to be
upgraded to supporting Token Binding at different times, providing a
smooth transition path for phasing in Token Binding. However, when
Token Binding has been performed, any Token Binding key mismatches
MUST be treated as fatal errors.
If all the participants in an authorization interaction support Token
Binding and yet one or more of them does not use it, this is likely
evidence of a downgrade attack. In this case, the authorization
SHOULD be aborted with an error. For instance, if the protected
resource knows that the authorization server and the user agent both
support Token Binding and yet the access token received does not
contain Token Binding information, this is almost certainly a sign of
an attack.
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The authorization server, client, and protected resource can
determine whether the others support Token Binding using the metadata
values defined in the next section. They can determine whether the
user agent supports Token Binding by whether it negotiated Token
Binding for the TLS connection.
5. Token Binding Metadata
5.1. Token Binding Client Metadata
Clients supporting Token Binding that also support the OAuth 2.0
Dynamic Client Registration Protocol [RFC7591] use these metadata
values to declare their support for Token Binding of access tokens
and refresh tokens:
client_access_token_token_binding_supported
OPTIONAL. Boolean value specifying whether the client supports
Token Binding of access tokens. If omitted, the default value is
"false".
client_refresh_token_token_binding_supported
OPTIONAL. Boolean value specifying whether the client supports
Token Binding of refresh tokens. If omitted, the default value is
"false".
5.2. Token Binding Authorization Server Metadata
Authorization servers supporting Token Binding that also support
OAuth 2.0 Authorization Server Metadata [OAuth.AuthorizationMetadata]
use these metadata values to declare their support for Token Binding
of access tokens and refresh tokens:
as_access_token_token_binding_supported
OPTIONAL. Boolean value specifying whether the authorization
server supports Token Binding of access tokens. If omitted, the
default value is "false".
as_refresh_token_token_binding_supported
OPTIONAL. Boolean value specifying whether the authorization
server supports Token Binding of refresh tokens. If omitted, the
default value is "false".
5.3. Token Binding Protected Resource Metadata
Protected resources supporting Token Binding that also support the
OAuth 2.0 Protected Resource Metadata [OAuth.ResourceMetadata] use
this metadata value to declare their support for Token Binding of
access tokens:
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resource_access_token_token_binding_supported
OPTIONAL. Boolean value specifying whether the protected resource
supports Token Binding of access tokens. If omitted, the default
value is "false".
6. Security Considerations
If a refresh request is received by the authorization server
containing a Referred Token Binding ID and the refresh token in the
request is not itself token bound, then it is not clear that token
binding the access token adds significant value. This situation
should be considered an open issue for discussion by the working
group.
7. IANA Considerations
7.1. OAuth Dynamic Client Registration Metadata Registration
This specification registers the following client metadata
definitions in the IANA "OAuth Dynamic Client Registration Metadata"
registry [IANA.OAuth.Parameters] established by [RFC7591]:
7.1.1. Registry Contents
o Client Metadata Name:
"client_access_token_token_binding_supported"
o Client Metadata Description: Boolean value specifying whether the
client supports Token Binding of access tokens
o Change Controller: IESG
o Specification Document(s): Section 5.1 of [[ this specification ]]
o Client Metadata Name:
"client_refresh_token_token_binding_supported"
o Client Metadata Description: Boolean value specifying whether the
client supports Token Binding of refresh tokens
o Change Controller: IESG
o Specification Document(s): Section 5.1 of [[ this specification ]]
7.2. OAuth Authorization Server Metadata Registration
This specification registers the following metadata definitions in
the IANA "OAuth Authorization Server Metadata" registry established
by [OAuth.AuthorizationMetadata]:
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7.2.1. Registry Contents
o Metadata Name: "as_access_token_token_binding_supported"
o Metadata Description: Boolean value specifying whether the
authorization server supports Token Binding of access tokens
o Change Controller: IESG
o Specification Document(s): Section 5.2 of [[ this specification ]]
o Metadata Name: "as_refresh_token_token_binding_supported"
o Metadata Description: Boolean value specifying whether the
authorization server supports Token Binding of refresh tokens
o Change Controller: IESG
o Specification Document(s): Section 5.2 of [[ this specification ]]
7.3. OAuth Protected Resource Metadata Registration
This specification registers the following client metadata definition
in the IANA "OAuth Protected Resource Metadata" registry
[IANA.OAuth.Parameters] established by [OAuth.ResourceMetadata]:
7.3.1. Registry Contents
o Resource Metadata Name:
"resource_access_token_token_binding_supported"
o Resource Metadata Description: Boolean value specifying whether
the protected resource supports Token Binding of access tokens
o Change Controller: IESG
o Specification Document(s): Section 5.3 of [[ this specification ]]
8. References
8.1. Normative References
[I-D.ietf-tokbind-https]
Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J.
Hodges, "Token Binding over HTTP", draft-ietf-tokbind-
https-06 (work in progress), August 2016.
[I-D.ietf-tokbind-protocol]
Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J.
Hodges, "The Token Binding Protocol Version 1.0", draft-
ietf-tokbind-protocol-10 (work in progress), September
2016.
[IANA.OAuth.Parameters]
IANA, "OAuth Parameters",
<http://www.iana.org/assignments/oauth-parameters>.
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[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>.
[OAuth.AuthorizationMetadata]
Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", draft-ietf-oauth-
discovery-04 (work in progress), August 2016,
<http://tools.ietf.org/html/
draft-ietf-oauth-discovery-04>.
[OAuth.ResourceMetadata]
Jones, M. and P. Hunt, "OAuth 2.0 Protected Resource
Metadata", draft-jones-oauth-resource-metadata-00 (work in
progress), August 2016, <http://tools.ietf.org/html/
draft-jones-oauth-resource-metadata-00>.
[OpenID.TokenBinding]
Jones, M., Bradley, J., and B. Campbell, "OpenID Connect
Token Bound Authentication 1.0", July 2016,
<http://openid.net/specs/
openid-connect-token-bound-authentication-1_0.html>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
RFC 7591, DOI 10.17487/RFC7591, July 2015,
<http://www.rfc-editor.org/info/rfc7591>.
[RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7662, DOI 10.17487/RFC7662, October 2015,
<http://www.rfc-editor.org/info/rfc7662>.
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[RFC7800] Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
Possession Key Semantics for JSON Web Tokens (JWTs)",
RFC 7800, DOI 10.17487/RFC7800, April 2016,
<http://www.rfc-editor.org/info/rfc7800>.
[SHS] National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-4, March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>.
8.2. Informative References
[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>.
[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, <http://www.rfc-editor.org/info/rfc7523>.
Appendix A. Acknowledgements
The authors would like to thank the following people for their
contributions to the specification: Dirk Balfanz, William Denniss,
Andrei Popov, and Nat Sakimura.
Appendix B. Open Issues
o What should we do in the case that a refresh request for a token
bound access token is received when the refresh token used in the
request is not token bound?
Appendix C. Document History
[[ to be removed by the RFC Editor before publication as an RFC ]]
-01
o Changed Token Binding for access tokens to use the Referred Token
Binding ID, now that the Implementation Considerations in the
Token Binding HTTPS specification make it clear that
implementations will enable using the Referred Token Binding ID.
o Defined Protected Resource Metadata value.
o Changed to use the more specific term "protected resource" instead
of "resource server".
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-00
o Created the initial working group version from draft-jones-oauth-
token-binding-00.
Authors' Addresses
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: http://self-issued.info/
John Bradley
Ping Identity
Email: ve7jtb@ve7jtb.com
URI: http://www.thread-safe.com/
Brian Campbell
Ping Identity
Email: brian.d.campbell@gmail.com
URI: https://twitter.com/__b_c
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