OAuth Working Group N. Sakimura
Internet-Draft Nomura Research Institute
Intended status: Standards Track K. Li
Expires: September 12, 2017 Alibaba Group
J. Bradley
Ping Identity
March 11, 2017
The OAuth 2.0 Authorization Framework: JWT Pop Token Usage
draft-sakimura-oauth-jpop-01
Abstract
This specification describes how to use JWT POP (Jpop) tokens that
were obtained through [POPKD] in HTTP requests to access OAuth 2.0
protected resources. Only the party in possession of a corresponding
cryptographic key with the Jpop token can use it to get access to the
associated resources unlike in the case of the bearer token described
in [RFC6750] where any party in posession of the access token can
access the resource.
Requirements Language
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 RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2017.
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Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Terms and definitions . . . . . . . . . . . . . . . . . . . . 3
3. JWT POP Token . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Sender Constrained Token . . . . . . . . . . . . . . . . . . 4
4.1. CN Constrained Token . . . . . . . . . . . . . . . . . . 4
4.2. Client ID Constrained Token . . . . . . . . . . . . . . . 5
5. Key Constrained Token . . . . . . . . . . . . . . . . . . . . 5
6. Resource access method . . . . . . . . . . . . . . . . . . . 7
6.1. Mutual TLS acess method . . . . . . . . . . . . . . . . . 7
6.2. Signature method . . . . . . . . . . . . . . . . . . . . 8
7. Authorization Error . . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.1. Jpop Authentication Scheme . . . . . . . . . . . . . . . 10
8.2. JWT Confirmation Methods . . . . . . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9.1. Certificate validation . . . . . . . . . . . . . . . . . 10
9.2. Key protection . . . . . . . . . . . . . . . . . . . . . 11
9.3. Audiance Restriction . . . . . . . . . . . . . . . . . . 11
9.4. Dynamic client registration elements . . . . . . . . . . 11
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Document History . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
This document specifies the method for the client to use a proof-of-
possestion token against a protected resource. The format of such
token is defined in section 3 of [RFC7800].
1.1. Notational 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].
Unless otherwise noted, all the protocol parameter names and values
are case sensitive.
2. Terms and definitions
For the purpose of this document, the terms defined in [RFC6749] and
[RFC7800] are used.
3. JWT POP Token
JWT PoP token is a JWS signed JWT whose payload is a JWT Claims Set.
The JWT claims set MUST include the following:
iss The issuer identifier of the auhtorization server.
aud The identifier of the resource server.
iat The issuance time of this token.
exp The expiry time of this token.
cnf The confirmation method.
Their semantics are defined in [RFC7519] and [RFC7800].
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Following is an example of such.
{
"iss": "https://server.example.com",
"aud": "https://resource.example.org",
"iat": "1360189224",
"exp": "1361398868",
"cnf":{...}
}
Figure 1: Example of JWT PoP Token.
4. Sender Constrained Token
There are several varieties of sender constrained token. Namely:
1. CN Constrained Token
2. Client ID Constrained Token
4.1. CN Constrained Token
CN constrained token is typically used when X.509 client certificate
authentication is used at the token endpoint. In this case, the
constraint is expressed by including the following member at the top
level of cnf claim.
cn The Common Name of the client certificate that the client used in
the authorization request.
The authorization server finds the relevant CN from the X.509 client
certificate authentication that is performed at the token endpoint.
{
"iss": "https://server.example.com",
"sub": "joe@example.com",
"aud": "https://resource.example.org",
"exp": "1361398824",
"nbf": "1360189224",
"cnf":{
"cn": "client.example.com"
}
Figure 2: Example of CN Constrained JWT.
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4.2. Client ID Constrained Token
The constraint in the Client ID constrained token is expressed by
including the following member at the top level of cnf claim.
cid The client_id of the client that the client used in the
authorization request. The combination of the "iss" of the access
token and this value forms a globally unique identifier for the
client.
The authorization server finds the client ID from the client ID used
in the client authentication at the token endpoint.
5. Key Constrained Token
Methods to express key constraints are extensively described in the
section 3 of [RFC7800]. Such cnf claim is used in the access token
described in section 3 to form a key constrained token. [RFC7800]
defines 4 confirmation methods.
jwk JSON Web Key Representing a Public Key
jwe Encrypted JSON Web Key
jwkt#s256 [RFC7638] Thumbprint of a JWK using the SHA-256 hash
function.
x5t#s256 [RFC7515] X.509 Certificate SHA-256 Thumbprint
jku JWK Set URL
Following is an example of a JWT payload containing a JWK with a raw
key.
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{
"iss": "https://server.example.com",
"sub": "joe@example.com",
"aud": "https://resource.example.org",
"exp": "1361398824",
"nbf": "1360189224",
"cnf":{
"jwk":{
"kty": "EC",
"use": "sig",
"crv": "P-256",
"x": "18wHLeIgW9wVN6VD1Txgpqy2LszYkMf6J8njVAibvhM",
"y": "-V4dS4UaLMgP_4fY4j8ir7cl1TXlFdAgcx55o7TkcSA"
}
}
}
Figure 3: Example of a JWK Key Constrained JWT.
Following is an example of a JWT payload containing a jku URI.
{
"iss": "https://server.example.com",
"sub": "joe@example.com",
"aud": "https://resource.example.org",
"exp": "1361398824",
"nbf": "1360189224",
"cnf":{
"jku": "https://client.example.com/keys/client123-jwks"
}
}
Figure 4: Example of a jku Constrained JWT.
Following is an example of a JWT payload containing a x5t#s256
Certificate Thumbprint of a x509 certificate. .
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{
"iss": "https://server.example.com",
"sub": "joe@example.com",
"aud": "https://resource.example.org",
"exp": "1361398824",
"nbf": "1360189224",
"cnf":{
"x5t#s256": "w5cK0ebwmCZUYDB2Y5SlESsXE8o9yZg05O89jdNidgI"
}
}
Figure 5: Example of a x5t#s256 Certificate Thumbprint Constrained
JWT.
6. Resource access method
The resource server that supports this specification MUST
authenticate the Client by having it demonstrate that it is the
holder of the key associated with the access token being used. The
confirmation method can be broadly categorized in two forms.
Mutual TLS method A method leveraging on the X.509 client
certificate authentication of the TLS connection. cn, x5t#s256,
and jku confirmation methods can be used with this access method.
(The JWKS referenced by the jku MUST contain JWK with x5c
certificate elements for this access method)
Signature method A method leveraging the signature on the nonce.
cid, jku, jwk, jwe, and, jwkt#S256 confirmation methods can be
used with this access method.
6.1. Mutual TLS acess method
CN cnf method Under this method, X.509 client certificate
authentication at the resource endpoint is being leveraged. The
resource endpoint MUST obtain the CN of the client certificate
used for the authentication and MUST verify that the value of the
cn member in the cnf member matches with it.
If it does not match, the process stops here and the resource
access MUST be denied.
If it is valid, then the resource server MUST verify the access
token. If it is valid, the resource SHOULD be returned as HTTP
response.
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x5t#s256 cnf method Under this method, X.509 client certificate
authentication at the resource endpoint is being leveraged. The
resource endpoint MUST obtain the client certificate used for the
authentication and MUST verify that the base64url-encoded SHA-256
thumprint of the DER encoded X.509 client certificate. The
x5t#s256 member in the cnf member MUST exactly match the
calculated thumbprint.
If it does not match, the process stops here and the resource
access MUST be denied.
If it is valid, then the resource server MUST verify the access
token. If it is valid, the resource SHOULD be returned as HTTP
response.
jku cnf method Under this method, X.509 client certificate
authentication at the resource endpoint is being leveraged. The
resource endpoint MUST obtain the client certificate used for the
authentication and MUST verify that the certificate matches one of
the x5c elements retrieved from the [RFC7517]JWKS. Each x5c
element may contain a chain of base64-encoded certificates. The
client certificate MUST only be compared with the last certificate
in the chain.
If it does not match, the process stops here and the resource
access MUST be denied.
If it is valid, then the resource server MUST verify the access
token. If it is valid, the resource SHOULD be returned as HTTP
response.
6.2. Signature method
For this, the following steps are taken:
1. The client prepares a nonce.
2. The client creates JWS compact serialization over the nonce.
To obtain it, first create a JSON with a name "nonce" and the value
being what was received in the previous step. The JWS MUST contain a
kid header element if the client has more than one signing key
published via JWKS URI e.g.,
{
"nonce":"dcd98b7102dd2f0e8b11d0f600bfb0c093"
}
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Then, "jws-on-nonce" is obtained by creating a compact serialization
of JWS on this JSON.
3. The client sends the request to the resource server, this time
with Authorization Request Header as defined in section 4.2 of
[RFC7235] with the credential as follows:
credentials = "Jpop" jpop-response
jpop-response = at-response "," s-response
at-response = "at" "=" access-token; As specified by [POPKD]
s-response = "s" "=" jws-on-nonce; Created in the step 3.
access-token = quoted-string
jws-on-nonce = quoted-string
In the following example, the access token and the jws-on-nonce are
represented as access.token.jwt and jws.of.nonce for the sake of
brevity.
GET /resource/1234 HTTP/1.0
Host: server.example.com
Authorization: Jpop at="access.token.jwt", s="jws.of.nonce"
Figure 6: Example resouce request
4. The resource server finds the client's public key form the access
token through the methods described in [RFC7800].
5. The resource server MUST verify the value of "s" of the
Authorization header. If it fails, the process stops here and the
resource access MUST be denied.
6. The resource server MUST verify the access token. If it is
valid, the resource SHOULD be returned as HTTP response.
7. Authorization Error
If the client requests the resource without the proper authoization
header, the resource server returns a HTTP 401 response with "WWW-
Authenticate" header as defined in section 4.1 of [RFC7235] with the
challenge as follows:
challenge = "Jpop" jpop-challenge
jpop-challenge = "nonce" "=" nonce-value
nonce-value = quoted-string
Following example depicts what the response would look like.
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HTTP/1.0 401 Unauthorized
Server: HTTPd/0.9
Date: Wed, 14 March 2017 09:26:53 GMT
WWW-Authenticate: Jpop nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093"
Figure 7: Example error response.
8. IANA Considerations
8.1. Jpop Authentication Scheme
A new scheme has been registered in the HTTP Authentication Scheme
Registry as follows:
Authentication Scheme Name: Jpop
Reference: Section 3 of this specification
Notes (optional): The Named Authentication scheme is intended to be
used only with OAuth Resource Access, and thus does not support proxy
authentication.
8.2. JWT Confirmation Methods
o Confirmation Method Value: "cn"
o Confirmation Method Description: CN match with the TLS client
auth.
o Change Controller: IESG
o Specification Document(s): This document.
o Confirmation Method Value: "cid"
o Confirmation Method Description: Client ID Confirmation
o Change Controller: IESG
o Specification Document(s): This document.
9. Security Considerations
9.1. Certificate validation
The "cn" JWT confirmation method relies its security property on the
X.509 client certificate authentication. In particular, the validity
of the certificate needs to be verified properly. It involves the
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traversal of all the certificate chain and the certificate validation
(e.g., with OCSP).
9.2. Key protection
The client's secret key must be kept securely. Otherwise, the notion
of PoP breaks down.
It should be noted that JWE confirmation method is significantly
weaker form of the PoP, as the resource server and the authorization
server can masquerade as the client.
9.3. Audiance Restriction
When using the signature method the client must specify to the AS the
aud it intends to send the token to, so that it can be included in
the AT.
A malicious RS could receive a AT with no aud or a logical audience
and then replay the AT and jws-on-nonce to the actual server.
NOTE another approach would be to include the resource in the jws-on-
nonce
9.4. Dynamic client registration elements
When a AS uses dynamic client registration it may accept software
statements supplied by a federation operator. Those software
statements can contain a JWKS-URI that is hosted by the federation
operator or protected by a certificate provisioned from a trusted
root. These methods would allow the federation operator to
administratively revoke the keys at the JWKS-URI without requiring
the JWKS to contain x5c elements with CA issued certificates and
having to have the RS perform full certificate validation for each
request.
10. Acknowledgements
The authors thank the following people for providing valuable
feedback to this document. Nov Matake (YAuth).
11. References
11.1. Normative References
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[POPKD] Bradley, J., Hunt, P., Jones, M., and H. Tschofenig,
"OAuth 2.0 Proof-of-Possession: Authorization Server to
Client Key Distribution", March 2017,
<https://tools.ietf.org/html/draft-ietf-oauth-pop-key-
distribution-03>.
[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>.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, DOI 10.17487/RFC2617, June 1999,
<http://www.rfc-editor.org/info/rfc2617>.
[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>.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<http://www.rfc-editor.org/info/rfc6750>.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Authentication", RFC 7235,
DOI 10.17487/RFC7235, June 2014,
<http://www.rfc-editor.org/info/rfc7235>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <http://www.rfc-editor.org/info/rfc7515>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<http://www.rfc-editor.org/info/rfc7517>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<http://www.rfc-editor.org/info/rfc7519>.
[RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK)
Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
2015, <http://www.rfc-editor.org/info/rfc7638>.
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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>.
11.2. Informative References
[PKCE] Sakimura, N., "Proof Key for Code Exchange by OAuth Public
Clients", July 2015.
[POPA] Hunt, P., Ed., "OAuth 2.0 Proof-of-Possession (PoP)
Security Architecture", March 2015,
<https://tools.ietf.org/html/draft-ietf-oauth-pop-
architecture-08>.
[TINTRO] Richer, J., "OAuth 2.0 Token Introspection", July 2015.
Appendix A. Document History
-00 Initial Version.
Authors' Addresses
Nat Sakimura
Nomura Research Institute
Otemachi Financial City Grand Cube, 1-9-2 Otemachi
Chiyoda-ku, Tokyo 100-0004
Japan
Phone: +81-3-5533-2111
Email: n-sakimura@nri.co.jp
URI: https://nat.sakimura.org/
Kepeng Li
Alibaba Group
Email: kepeng.lkp@alibaba-inc.com
John Bradley
Ping Identity
Email: ve7jtb@ve7jtb.com
URI: http://www.thread-safe.com/
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