Internet DRAFT - draft-ietf-oauth-token-binding
draft-ietf-oauth-token-binding
OAuth Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track B. Campbell
Expires: April 22, 2019 Ping Identity
J. Bradley
Yubico
W. Denniss
Google
October 19, 2018
OAuth 2.0 Token Binding
draft-ietf-oauth-token-binding-08
Abstract
This specification enables OAuth 2.0 implementations to apply Token
Binding to Access Tokens, Authorization Codes, Refresh Tokens, JWT
Authorization Grants, and JWT Client Authentication. This
cryptographically binds these tokens to a client's Token Binding key
pair, possession of which is proven on the TLS connections over which
the tokens 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
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
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This Internet-Draft will expire on April 22, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation and Conventions . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Token Binding for Refresh Tokens . . . . . . . . . . . . . . 4
2.1. Example Token Binding for Refresh Tokens . . . . . . . . 4
3. Token Binding for Access Tokens . . . . . . . . . . . . . . . 6
3.1. Access Tokens Issued from the Authorization Endpoint . . 7
3.1.1. Example Access Token Issued from the Authorization
Endpoint . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Access Tokens Issued from the Token Endpoint . . . . . . 9
3.2.1. Example Access Token Issued from the Token Endpoint . 9
3.3. Protected Resource Token Binding Validation . . . . . . . 11
3.3.1. Example Protected Resource Request . . . . . . . . . 11
3.4. Representing Token Binding in JWT Access Tokens . . . . . 11
3.5. Representing Token Binding in Introspection Responses . . 12
4. Token Binding Metadata . . . . . . . . . . . . . . . . . . . 13
4.1. Token Binding Client Metadata . . . . . . . . . . . . . . 13
4.2. Token Binding Authorization Server Metadata . . . . . . . 13
5. Token Binding for Authorization Codes . . . . . . . . . . . . 14
5.1. Native Application Clients . . . . . . . . . . . . . . . 14
5.1.1. Code Challenge . . . . . . . . . . . . . . . . . . . 14
5.1.1.1. Example Code Challenge . . . . . . . . . . . . . 15
5.1.2. Code Verifier . . . . . . . . . . . . . . . . . . . . 15
5.1.2.1. Example Code Verifier . . . . . . . . . . . . . . 16
5.2. Web Server Clients . . . . . . . . . . . . . . . . . . . 16
5.2.1. Code Challenge . . . . . . . . . . . . . . . . . . . 17
5.2.1.1. Example Code Challenge . . . . . . . . . . . . . 17
5.2.2. Code Verifier . . . . . . . . . . . . . . . . . . . . 18
5.2.2.1. Example Code Verifier . . . . . . . . . . . . . . 18
6. Token Binding JWT Authorization Grants and Client
Authentication . . . . . . . . . . . . . . . . . . . . . . . 19
6.1. JWT Format and Processing Requirements . . . . . . . . . 19
6.2. Token Bound JWTs for Client Authentication . . . . . . . 20
6.3. Token Bound JWTs for as Authorization Grants . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7.1. Phasing in Token Binding . . . . . . . . . . . . . . . . 21
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7.2. Binding of Refresh Tokens . . . . . . . . . . . . . . . . 21
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
8.1. OAuth Dynamic Client Registration Metadata Registration . 22
8.1.1. Registry Contents . . . . . . . . . . . . . . . . . . 22
8.2. OAuth Authorization Server Metadata Registration . . . . 23
8.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 23
8.3. PKCE Code Challenge Method Registration . . . . . . . . . 23
8.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 23
9. Token Endpoint Authentication Method Registration . . . . . . 23
9.1. Registry Contents . . . . . . . . . . . . . . . . . . . . 24
10. Sub-Namespace Registrations . . . . . . . . . . . . . . . . . 24
10.1. Registry Contents . . . . . . . . . . . . . . . . . . . 24
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
11.1. Normative References . . . . . . . . . . . . . . . . . . 24
11.2. Informative References . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 27
Appendix B. Document History . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
This specification enables OAuth 2.0 [RFC6749] implementations to
apply Token Binding (TLS Extension for Token Binding Protocol
Negotiation [RFC8472], The Token Binding Protocol Version 1.0
[RFC8471] and Token Binding over HTTP [RFC8473]) to Access Tokens,
Authorization Codes, Refresh Tokens, JWT Authorization Grants, and
JWT Client Authentication. This cryptographically binds these tokens
to a client's Token Binding key pair, possession of which is proven
on the TLS connections over which the tokens are intended to be used.
This use of Token Binding protects these tokens from man-in-the-
middle and token export and replay attacks.
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Terminology
This specification uses the terms "Access Token", "Authorization
Code", "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
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Binding" and "Token Binding ID" defined by Token Binding over HTTP
[RFC8473].
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 [RFC8473]. It cryptographically binds the refresh token to the
client's Token Binding key pair, possession of which is proven on the
TLS connections 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 federation use cases described in Token Binding
over HTTP [RFC8473], Section 4, 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,
provided it is integrity-protected, 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.
2.1. Example Token Binding for Refresh Tokens
This section provides an example of what the interactions around a
Token Bound refresh token might look like, along with some details of
the involved processing. Token Binding of refresh tokens is most
useful for native application clients so the example has protocol
elements typical of a native client flow. Extra line breaks in all
examples are for display purposes only.
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A native application client makes the following access token request
with an authorization code using a TLS connection where Token Binding
has been negotiated. A PKCE "code_verifier" is included because use
of PKCE is considered best practice for native application clients
[BCP212]. The base64url-encoded representation of the exported
keying material (EKM) from that TLS connection is
"p6ZuSwfl6pIe8es5KyeV76T4swZmQp0_awd27jHfrbo", which is needed to
validate the Token Binding Message.
POST /as/token.oauth2 HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
Sec-Token-Binding: AIkAAgBBQGto7hHRR0Y5nkOWqc9KNfwW95dEFmSI_tCZ_Cbl
7LWlt6Xjp3DbjiDJavGFiKP2HV_2JSE42VzmKOVVV8m7eqAAQOKiDK1Oi0z6v4X5B
P7uc0pFestVZ42TTOdJmoHpji06Qq3jsCiCRSJx9ck2fWJYx8tLVXRZPATB3x6c24
aY0ZEAAA
grant_type=authorization_code&code=4bwcZesc7Xacc330ltc66Wxk8EAfP9j2
&code_verifier=2x6_ylS390-8V7jaT9wj.8qP9nKmYCf.V-rD9O4r_1
&client_id=example-native-client-id
Figure 1: Initial Request with Code
A refresh token is issued in response to the prior request. Although
it looks like a typical response to the client, the authorization
server has bound the refresh token to the Provided Token Binding ID
from the encoded Token Binding message in the "Sec-Token-Binding"
header of the request. In this example, that binding is done by
saving the Token Binding ID alongside other information about the
refresh token in some server side persistent storage. The base64url-
encoded representation of that Token Binding ID is "AgBBQGto7hHRR0Y5n
kOWqc9KNfwW95dEFmSI_tCZ_Cbl7LWlt6Xjp3DbjiDJavGFiKP2HV_2JSE42VzmKOVVV8
m7eqA".
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-cache, no-store
{
"access_token":"EdRs7qMrLb167Z9fV2dcwoLTC",
"refresh_token":"ACClZEIQTjW9arT9GOJGGd7QNwqOMmUYfsJTiv8his4",
"token_type":"Bearer",
"expires_in":3600
}
Figure 2: Successful Response
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When the access token expires, the client requests a new one with a
refresh request to the token endpoint. In this example, the request
is made on a new TLS connection so the EKM (base64url-encoded: "va-
84Ukw4Zqfd7uWOtFrAJda96WwgbdaPDX2knoOiAE") and signature in the Token
Binding Message are different than in the initial request.
POST /as/token.oauth2 HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
Sec-Token-Binding: AIkAAgBBQGto7hHRR0Y5nkOWqc9KNfwW95dEFmSI_tCZ_Cbl
7LWlt6Xjp3DbjiDJavGFiKP2HV_2JSE42VzmKOVVV8m7eqAAQCpGbaG_YRf27qOra
L0UT4fsKKjL6PukuOT00qzamoAXxOq7m_id7O3mLpnb_sM7kwSxLi7iNHzzDgCAkP
t3lHwAAA
refresh_token=ACClZEIQTjW9arT9GOJGGd7QNwqOMmUYfsJTiv8his4
&grant_type=refresh_token&client_id=example-native-client-id
Figure 3: Refresh Request
However, because the Token Binding ID is long-lived and may span
multiple TLS sessions and connections, it is the same as in the
initial request. That Token Binding ID is what the refresh token is
bound to, so the authorization server is able to verify it and issue
a new access token.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-cache, no-store
{
"access_token":"bwcESCwC4yOCQ8iPsgcn117k7",
"token_type":"Bearer",
"expires_in":3600
}
Figure 4: Successful Response
3. Token Binding for Access Tokens
Token Binding for access tokens cryptographically binds the access
token to the client's Token Binding key pair, possession of which is
proven on the TLS connections between the client and the protected
resource. Token Binding is applied to access tokens in a similar
manner to that described in Token Binding over HTTP [RFC8473],
Section 4 (Federation Use Cases). It also builds upon the mechanisms
for Token Binding of ID Tokens defined in OpenID Connect Token Bound
Authentication 1.0 [OpenID.TokenBinding].
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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 Implementation Considerations of
Token Binding over HTTP [RFC8473], Section 6.
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
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 OAuth 2.0 [RFC6749],
Section 4.2, the Token Binding ID of the client's TLS channel to the
protected resource is sent with the authorization request as the
Referred Token Binding ID in the "Sec-Token-Binding" header, and is
used to Token Bind the access token.
Upon receiving the Referred Token Binding ID in an authorization
request, the authorization server associates (Token Binds) the ID
with the access token in a way that can be accessed by the protected
resource. Such methods include embedding the Referred Token Binding
ID (or a cryptographic hash of it) in the issued access token itself,
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possibly using the syntax described in Section 3.4, or through token
introspection as described in Section 3.5. The method for
associating the referred token binding ID with the access token is
determined by the authorization server and the protected resource,
and is beyond the scope for this specification.
3.1.1. Example Access Token Issued from the Authorization Endpoint
This section provides an example of what the interactions around a
Token Bound access token issued from the authorization endpoint might
look like, along with some details of the involved processing. Extra
line breaks in all examples are for display purposes only.
The client directs the user-agent to make the following HTTP request
to the authorization endpoint. It is a typical authorization request
that, because Token Binding was negotiated on the underlying TLS
connection and the user-agent was signaled to reveal the Referred
Token Binding, also includes the "Sec-Token-Binding" header with a
Token Binding Message that contains both a Provided and Referred
Token Binding. The base64url-encoded EKM from the TLS connection
over which the request was made is
"jI5UAyjs5XCPISUGQIwgcSrOiVIWq4fhLVIFTQ4nLxc".
GET /as/authorization.oauth2?response_type=token
&client_id=example-client-id&state=rM8pZxG1c3gKy6rEbsD8s
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Eorg%2Fcb HTTP/1.1
Host: server.example.com
Sec-Token-Binding: ARIAAgBBQIEE8mSMtDy2dj9EEBdXaQT9W3Rq1NS-jW8ebPoF
6FyL0jIfATVE55zlircgOTZmEg1xeIrC3DsGegwjs4bhw14AQGKDlAXFFMyQkZegC
wlbTlqX3F9HTt-lJxFU_pi16ezka7qVRCpSF0BQLfSqlsxMbYfSSCJX1BDtrIL7PX
j__fUAAAECAEFA1BNUnP3te5WrwlEwiejEz0OpesmC5PElWc7kZ5nlLSqQTj1ciIp
5vQ30LLUCyM_a2BYTUPKtd5EdS-PalT4t6ABADgeizRa5NkTMuX4zOdC-R4cLNWVV
O8lLu2Psko-UJLR_XAH4Q0H7-m0_nQR1zBN78nYMKPvHsz8L3zWKRVyXEgAA
Figure 5: Authorization Request
The authorization server issues an access token and delivers it to
the client by redirecting the user-agent with the following HTTP
response:
HTTP/1.1 302 Found
Location: https://client.example.org/cb#state=rM8pZxG1c3gKy6rEbsD8s
&expires_in=3600&token_type=Bearer
&access_token=eyJhbGciOiJFUzI[...omitted for brevity...]8xy5W5sQ
Figure 6: Authorization Response
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The access token is bound to the Referred Token Binding ID from the
authorization request, which when represented as a JWT, as described
in Section 3.4, contains the SHA-256 hash of the Token Binding ID as
the value of the "tbh" (token binding hash) member of the "cnf"
(confirmation) claim. The confirmation claim portion of the JWT
Claims Set is shown in the following figure.
{
...other claims omitted for brevity...
"cnf":{
"tbh": "vowQESa_MgbGJwIXaFm_BTN2QDPwh8PhuBm-EtUAqxc"
}
}
Figure 7: Confirmation Claim
3.2. Access Tokens Issued from the Token Endpoint
For access tokens returned from the token endpoint, the Token Binding
ID of the client's TLS channel to the protected resource is sent as
the Referred Token Binding ID in the "Sec-Token-Binding" header, and
is used to Token Bind the access token. This applies to all the
grant types from OAuth 2.0 [RFC6749] using the token endpoint,
including, but not limited to the refresh and authorization code
token requests, as well as some extension grants, such as JWT
assertion authorization grants [RFC7523].
Upon receiving the Referred Token Binding ID in a token request, the
authorization server associates (Token Binds) the ID with the access
token in a way that can be accessed by the protected resource. Such
methods include embedding the Referred Token Binding ID (or a
cryptographic hash of it) in the issued access token itself, possibly
using the syntax described in Section 3.4, or through token
introspection as described in Section 3.5. The method for
associating the referred token binding ID with the access token is
determined by the authorization server and the protected resource,
and is beyond the scope for this specification.
Note that if the request results in a new refresh token being
generated, it can be Token bound using the Provided Token Binding ID,
per Section 2.
3.2.1. Example Access Token Issued from the Token Endpoint
This section provides an example of what the interactions around a
Token Bound access token issued from the token endpoint might look
like, along with some details of the involved processing. Extra line
breaks in all examples are for display purposes only.
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The client makes an access token request to the token endpoint and
includes the "Sec-Token-Binding" header with a Token Binding Message
that contains both Provided and Referred Token Binding IDs. The
Provided Token Binding ID is used to validate the token binding of
the refresh token in the request (and to Token Bind a new refresh
token, if one is issued), and the Referred Token Binding ID is used
to Token Bind the access token that is generated. The base64url-
encoded EKM from the TLS connection over which the access token
request was made is "4jTc5e1QpocqPTZ5l6jsb6pRP18IFKdwwPvasYjn1-E".
POST /as/token.oauth2 HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
Sec-Token-Binding: ARIAAgBBQJFXJir2w4gbJ7grBx9uTYWIrs9V50-PW4ZijegQ
0LUM-_bGnGT6DizxUK-m5n3dQUIkeH7ybn6wb1C5dGyV_IAAQDDFToFrHt41Zppq7
u_SEMF_E-KimAB-HewWl2MvZzAQ9QKoWiJCLFiCkjgtr1RrA2-jaJvoB8o51DTGXQ
ydWYkAAAECAEFAuC1GlYU83rqTGHEau1oqvNwy0fDsdXzIyT_4x1FcldsMxjFkJac
IBJFGuYcccvnCak_duFi3QKFENuwxql-H9ABAMcU7IjJOUA4IyE6YoEcfz9BMPQqw
M5M6hw4RZNQd58fsTCCslQE_NmNCl9JXy4NkdkEZBxqvZGPr0y8QZ_bmAwAA
refresh_token=gZR_ZI8EAhLgWR-gWxBimbgZRZi_8EAhLgWRgWxBimbf
&grant_type=refresh_token&client_id=example-client-id
Figure 8: Access Token Request
The authorization server issues an access token bound to the Referred
Token Binding ID and delivers it in a response the client.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-cache, no-store
{
"access_token":"eyJhbGciOiJFUzI1NiIsImtp[...omitted...]1cs29j5c3",
"token_type":"Bearer",
"expires_in":3600
}
Figure 9: Response
The access token is bound to the Referred Token Binding ID of the
access token request, which when represented as a JWT, as described
in Section 3.4, contains the SHA-256 hash of the Token Binding ID as
the value of the "tbh" (token binding hash) member of the "cnf"
(confirmation) claim. The confirmation claim portion of the JWT
Claims Set of the access token is shown in the following figure.
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{
...other claims omitted for brevity...
"cnf":{
"tbh": "7NRBu9iDdJlYCTOqyeYuLxXv0blEA-yTpmGIrAwKAws"
}
}
Figure 10: Confirmation Claim
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.
3.3.1. Example Protected Resource Request
For example, a protected resource request using the access token from
Section 3.2.1 would look something like the following. The
base64url-encoded EKM from the TLS connection over which the request
was made is "7LsNP3BT1aHHdXdk6meEWjtSkiPVLb7YS6iHp-JXmuE". The
protected resource validates the binding by comparing the Provided
Token Binding ID from the "Sec-Token-Binding" header to the token
binding hash confirmation of the access token. Extra line breaks in
the example are for display purposes only.
GET /api/stuff HTTP/1.1
Host: resource.example.org
Authorization: Bearer eyJhbGciOiJFUzI1NiIsI[...omitted...]1cs29j5c3
Sec-Token-Binding: AIkAAgBBQLgtRpWFPN66kxhxGrtaKrzcMtHw7HV8yMk_-MdR
XJXbDMYxZCWnCASRRrmHHHL5wmpP3bhYt0ChRDbsMapfh_QAQN1He3Ftj4Wa_S_fz
ZVns4saLfj6aBoMSQW6rLs19IIvHze7LrGjKyCfPTKXjajebxp-TLPFZCc0JTqTY5
_0MBAAAA
Figure 11: Protected Resource Request
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"
member is the base64url encoding of the SHA-256 hash of the Token
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Binding ID. All trailing pad '=' characters are omitted from the
encoded value and no line breaks, whitespace, or other additional
characters are included.
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.org",
"sub": "brian@example.com"
"iat": 1467324320,
"exp": 1467324920,
"cnf":{
"tbh": "7NRBu9iDdJlYCTOqyeYuLxXv0blEA-yTpmGIrAwKAws"
}
}
Figure 12: JWT with Token Binding Hash Confirmation Claim
3.5. Representing Token Binding in Introspection Responses
OAuth 2.0 Token Introspection [RFC7662] defines a method for a
protected resource to query an authorization server about the active
state of an access token as well as to determine meta-information
about the token.
For a token bound access token, the hash of the Token Binding ID to
which the token is bound is conveyed to the protected resource as
meta-information in a token introspection response. The hash is
conveyed using same structure as the token binding hash confirmation
method, described in Section 3.4, as a top-level member of the
introspection response JSON. The protected resource compares that
token binding hash to a hash of the provided Token Binding ID and
rejects the request, if they do not match.
The following is an example of an introspection response for an
active token bound access token with a "tbh" token binding hash
confirmation method.
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HTTP/1.1 200 OK
Content-Type: application/json
{
"active": true,
"iss": "https://server.example.com",
"aud": "https://resource.example.org",
"sub": "brian@example.com"
"iat": 1467324320,
"exp": 1467324920,
"cnf":{
"tbh": "7NRBu9iDdJlYCTOqyeYuLxXv0blEA-yTpmGIrAwKAws"
}
}
Figure 13: Example Introspection Response for a Token Bound Access
Token
4. Token Binding Metadata
4.1. 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". Authorization servers MUST NOT Token Bind refresh tokens
issued to a client that does not support Token Binding of refresh
tokens, but MAY reject requests completely from such clients if
token binding is required by authorization server policy by
returning an OAuth error response.
4.2. Token Binding Authorization Server Metadata
Authorization servers supporting Token Binding that also support
OAuth 2.0 Authorization Server Metadata [RFC8414] use these metadata
values to declare their support for Token Binding of access tokens
and refresh tokens:
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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. Token Binding for Authorization Codes
There are two variations for Token Binding of an authorization code.
One is appropriate for native application clients and the other for
web server clients. The nature of where the various components
reside for the different client types demands different methods of
Token Binding the authorization code so that it is bound to a Token
Binding key on the end user's device. This ensures that a lost or
stolen authorization code cannot be successfully utilized from a
different device. For native application clients, the code is bound
to a Token Binding key pair that the native client itself possesses.
For web server clients, the code is bound to a Token Binding key pair
on the end user's browser. Both variations utilize the extensible
framework of Proof Key for Code Exchange (PKCE) [RFC7636], which
enables the client to show possession of a certain key when
exchanging the authorization code for tokens. The following
subsections individually describe each of the two PKCE methods
respectively.
5.1. Native Application Clients
This section describes a PKCE method suitable for native application
clients that cryptographically binds the authorization code to a
Token Binding key pair on the client, which the client proves
possession of on the TLS connection during the access token request
containing the authorization code. The authorization code is bound
to the Token Binding ID that the native application client uses to
resolve the authorization code at the token endpoint. This binding
ensures that the client that made the authorization request is the
same client that is presenting the authorization code.
5.1.1. Code Challenge
As defined in Proof Key for Code Exchange [RFC7636], the client sends
the code challenge as part of the OAuth 2.0 authorization request
with the two additional parameters: "code_challenge" and
"code_challenge_method".
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For this Token Binding method of PKCE, "TB-S256" is used as the value
of the "code_challenge_method" parameter.
The value of the "code_challenge" parameter is the base64url encoding
(per Section 5 of [RFC4648] with all trailing padding ('=')
characters omitted and without the inclusion of any line breaks or
whitespace) of the SHA-256 hash of the Provided Token Binding ID that
the client will use when calling the authorization server's token
endpoint. Note that, prior to making the authorization request, the
client may need to establish a TLS connection between itself and the
authorization server's token endpoint in order to establish the
appropriate Token Binding ID.
When the authorization server issues the authorization code in the
authorization response, it associates the code challenge and method
values with the authorization code so they can be verified later when
the authorization code is presented in the access token request.
5.1.1.1. Example Code Challenge
For example, a native application client sends an authorization
request by sending the user's browser to the authorization endpoint.
The resulting HTTP request looks something like the following (with
extra line breaks for display purposes only).
GET /as/authorization.oauth2?response_type=code
&client_id=example-native-client-id&state=oUC2jyYtzRCrMyWrVnGj
&code_challenge=rBlgOyMY4teiuJMDgOwkrpsAjPyI07D2WsEM-dnq6eE
&code_challenge_method=TB-S256 HTTP/1.1
Host: server.example.com
Figure 14: Authorization Request with PKCE Challenge
5.1.2. Code Verifier
Upon receipt of the authorization code, the client sends the access
token request to the token endpoint. The Token Binding Protocol
[RFC8471] is negotiated on the TLS connection between the client and
the authorization server and the "Sec-Token-Binding" header, as
defined in Token Binding over HTTP [RFC8473], is included in the
access token request. The authorization server extracts the Provided
Token Binding ID from the header value, hashes it with SHA-256, and
compares it to the "code_challenge" value previously associated with
the authorization code. If the values match, the token endpoint
continues processing as normal (as defined by OAuth 2.0 [RFC6749]).
If the values do not match, an error response indicating
"invalid_grant" MUST be returned.
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The "Sec-Token-Binding" header contains sufficient information for
verification of the authorization code and its association to the
original authorization request. However, PKCE [RFC7636] requires
that a "code_verifier" parameter be sent with the access token
request, so the static value "provided_tb" is used to meet that
requirement and indicate that the Provided Token Binding ID is used
for the verification.
5.1.2.1. Example Code Verifier
An example access token request, correlating to the authorization
request in the previous example, to the token endpoint over a TLS
connection for which Token Binding has been negotiated would look
like the following (with extra line breaks for display purposes
only). The base64url-encoded EKM from the TLS connection over which
the request was made is
"pNVKtPuQFvylNYn000QowWrQKoeMkeX9H32hVuU71Bs".
POST /as/token.oauth2 HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
Sec-Token-Binding: AIkAAgBBQEOO9GRFP-LM0hoWw6-2i318BsuuUum5AL8bt1sz
lr1EFfp5DMXMNW3O8WjcIXr2DKJnI4xnuGsE6GywQd9RbD0AQJDb3xyo9PBxj8M6Y
jLt-6OaxgDkyoBoTkyrnNbLc8tJQ0JtXomKzBbj5qPtHDduXc6xz_lzvNpxSPxi42
8m7wkAAA
grant_type=authorization_code&code=mJAReTWKX7zI3oHUNd4o3PeNqNqxKGp6
&code_verifier=provided_tb&client_id=example-native-client-id
Figure 15: Token Request with PKCE Verifier
5.2. Web Server Clients
This section describes a PKCE method suitable for web server clients,
which cryptographically binds the authorization code to a Token
Binding key pair on the browser. The authorization code is bound to
the Token Binding ID that the browser uses to deliver the
authorization code to a web server client, which is sent to the
authorization server as the Referred Token Binding ID during the
authorization request. The web server client conveys the Token
Binding ID to the authorization server when making the access token
request containing the authorization code. This binding ensures that
the authorization code cannot successfully be played or replayed to
the web server client from a different browser than the one that made
the authorization request.
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5.2.1. Code Challenge
As defined in Proof Key for Code Exchange [RFC7636], the client sends
the code challenge as part of the OAuth 2.0 Authorization Request
with the two additional parameters: "code_challenge" and
"code_challenge_method".
The client must send the authorization request through the browser
such that the Token Binding ID established between the browser and
itself is revealed to the authorization server's authorization
endpoint as the Referred Token Binding ID. Typically, this is done
with an HTTP redirection response and the "Include-Referred-Token-
Binding-ID" header, as defined in Token Binding over HTTP [RFC8473],
Section 5.3.
For this Token Binding method of PKCE, "referred_tb" is used for the
value of the "code_challenge_method" parameter.
The value of the "code_challenge" parameter is "referred_tb". The
static value for the required PKCE parameter indicates that the
authorization code is to be bound to the Referred Token Binding ID
from the Token Binding Message sent in the "Sec-Token-Binding" header
of the authorization request.
When the authorization server issues the authorization code in the
authorization response, it associates the Token Binding ID (or hash
thereof) and code challenge method with the authorization code so
they can be verified later when the authorization code is presented
in the access token request.
5.2.1.1. Example Code Challenge
For example, the web server client sends the authorization request by
redirecting the browser to the authorization endpoint. That HTTP
redirection response looks like the following (with extra line breaks
for display purposes only).
HTTP/1.1 302 Found
Location: https://server.example.com?response_type=code
&client_id=example-web-client-id&state=P4FUFqYzs1ij3ffsYCP34d3
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Eorg%2Fcb
&code_challenge=referred_tb&code_challenge_method=referred_tb
Include-Referred-Token-Binding-ID: true
Figure 16: Redirect the Browser
The redirect includes the "Include-Referred-Token-Binding-ID"
response header field that signals to the user-agent that it should
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reveal, to the authorization server, the Token Binding ID used on the
connection to the web server client. The resulting HTTP request to
the authorization server looks something like the following (with
extra line breaks for display purposes only). The base64url-encoded
EKM from the TLS connection over which the request was made is
"7gOdRzMhPeO-1YwZGmnVHyReN5vd2CxcsRBN69Ue4cI".
GET /as/authorization.oauth2?response_type=code
&client_id=example-web-client-id&state=dryo8YFpWacbUPjhBf4Nvt51
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Eorg%2Fcb
&code_challenge=referred_tb
&code_challenge_method=referred_tb HTTP/1.1
Host: server.example.com
Sec-Token-Binding: ARIAAgBBQB-XOPf5ePlf7ikATiAFEGOS503lPmRfkyymzdWw
HCxl0njjxC3D0E_OVfBNqrIQxzIfkF7tWby2ZfyaE6XpwTsAQBYqhFX78vMOgDX_F
d_b2dlHyHlMmkIz8iMVBY_reM98OUaJFz5IB7PG9nZ11j58LoG5QhmQoI9NXYktKZ
RXxrYAAAECAEFAdUFTnfQADkn1uDbQnvJEk6oQs38L92gv-KO-qlYadLoDIKe2h53
hSiKwIP98iRj_unedkNkAMyg9e2mY4Gp7WwBAeDUOwaSXNz1e6gKohwN4SAZ5eNyx
45Mh8VI4woL1BipLoqrJRoK6dxFkWgHRMuBROcLGUj5PiOoxybQH_Tom3gAA
Figure 17: Authorization Request
5.2.2. Code Verifier
The web server client receives the authorization code from the
browser and extracts the Provided Token Binding ID from the "Sec-
Token-Binding" header of the request. The client sends the
base64url-encoded (per Section 5 of [RFC4648] with all trailing
padding ('=') characters omitted and without the inclusion of any
line breaks or whitespace) Provided Token Binding ID as the value of
the "code_verifier" parameter in the access token request to the
authorization server's token endpoint. The authorization server
compares the value of the "code_verifier" parameter to the Token
Binding ID value previously associated with the authorization code.
If the values match, the token endpoint continues processing as
normal (as defined by OAuth 2.0 [RFC6749]). If the values do not
match, an error response indicating "invalid_grant" MUST be returned.
5.2.2.1. Example Code Verifier
Continuing the example from the previous section, the authorization
server sends the code to the web server client by redirecting the
browser to the client's "redirect_uri", which results in the browser
making a request like the following (with extra line breaks for
display purposes only) to the web server client over a TLS channel
for which Token Binding has been established. The base64url-encoded
EKM from the TLS connection over which the request was made is
"EzW60vyINbsb_tajt8ij3tV6cwy2KH-i8BdEMYXcNn0".
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GET /cb?state=dryo8YFpWacbUPjhBf4Nvt51&code=jwD3oOa5cQvvLc81bwc4CMw
Host: client.example.org
Sec-Token-Binding: AIkAAgBBQHVBU530AA5J9bg20J7yRJOqELN_C_doL_ijvqpW
GnS6AyCntoed4UoisCD_fIkY_7p3nZDZADMoPXtpmOBqe1sAQEwgC9Zpg7QFCDBib
6GlZki3MhH32KNfLefLJc1vR1xE8l7OMfPLZHP2Woxh6rEtmgBcAABubEbTz7muNl
Ln8uoAAA
Figure 18: Authorization Response to Web Server Client
The web server client takes the Provided Token Binding ID from the
above request from the browser and sends it, base64url encoded, to
the authorization server in the "code_verifier" parameter of the
authorization code grant type request. Extra line breaks in the
example request are for display purposes only.
POST /as/token.oauth2 HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
Authorization: Basic b3JnLmV4YW1wbGUuY2xpZW50OmlldGY5OGNoaWNhZ28=
grant_type=authorization_code&code=jwD3oOa5cQvvLc81bwc4CMw
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Eorg%2Fcb
&client_id=example-web-client-id
&code_verifier=AgBBQHVBU530AA5J9bg20J7yRJOqELN_C_doL_ijv
qpWGnS6AyCntoed4UoisCD_fIkY_7p3nZDZADMoPXtpmOBqe1s
Figure 19: Exchange Authorization Code
6. Token Binding JWT Authorization Grants and Client Authentication
The JWT Profile for OAuth 2.0 Client Authentication and Authorization
Grants [RFC7523] defines the use of bearer JWTs as a means for
requesting an OAuth 2.0 access token as well as for client
authentication. This section describes extensions to that
specification enabling the application of Token Binding to JWT client
authentication and JWT authorization grants.
6.1. JWT Format and Processing Requirements
In addition the requirements set forth in Section 3 of RFC 7523
[RFC7523], the following criteria must also be met for token bound
JWTs used as authorization grants or for client authentication.
o The JWT MUST contain a "cnf" (confirmation) claim with a "tbh"
(token binding hash) member identifying the Token Binding ID of
the Provided Token Binding used by the client on the TLS
connection to the authorization server. The authorization server
MUST reject any JWT that has a token binding hash confirmation
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that does not match the corresponding hash of the Provided Token
Binding ID from the "Sec-Token-Binding" header of the request.
6.2. Token Bound JWTs for Client Authentication
To use a token bound JWT for client authentication, the client uses
the parameter values and encodings from Section 2.2 of RFC 7523
[RFC7523] with one exception: the value of the
"client_assertion_type" is "urn:ietf:params:oauth:client-assertion-
type:jwt-token-bound".
The "OAuth Token Endpoint Authentication Methods" registry
[IANA.OAuth.Parameters] contains values, each of which specify a
method of authenticating a client to the authorization server. The
values are used to indicated supported and utilized client
authentication methods in authorization server metadata, such as
[OpenID.Discovery] and [RFC8414], and in OAuth 2.0 Dynamic Client
Registration Protocol [RFC7591]. The values "private_key_jwt" and
"client_secret_jwt" are designated by OpenID Connect [OpenID.Core] as
authentication method values for bearer JWT client authentication
using asymmetric and symmetric JWS [RFC7515] algorithms respectively.
For Token Bound JWT for client authentication, this specification
defines and registers the following authentication method values.
private_key_token_bound_jwt
Indicates that client authentication to the authorization server
will occur with a Token Bound JWT, which is signed with a client's
private key.
client_secret_token_bound_jwt
Indicates that client authentication to the authorization server
will occur with a Token Bound JWT, which is integrity protected
with a MAC using the octets of the UTF-8 representation of the
client secret as the shared key.
Note that just as with the "private_key_jwt" and "client_secret_jwt"
authentication methods, the "token_endpoint_auth_signing_alg" client
registration parameter may be used to indicate the JWS algorithm used
for signing the client authentication JWT for the authentication
methods defined above.
6.3. Token Bound JWTs for as Authorization Grants
To use a token bound JWT for an authorization grant, the client uses
the parameter values and encodings from Section 2.1 of RFC 7523
[RFC7523] with one exception: the value of the "grant_type" is
"urn:ietf:params:oauth:grant-type:jwt-token-bound".
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7. Security Considerations
7.1. Phasing in Token Binding
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 the omission of Token Binding at any step as a fatal
error. 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, for some
reasonable period of time during which Token Binding technology is
being adopted, 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.
In more controlled deployment environments where the participants in
an authorization interaction are known or expected to support Token
Binding and yet one or more of them does not use it, the
authorization SHOULD be aborted with an error. For instance, an
authorization server should reject a token request that does not
include the "Sec-Token-Binding" header, if the request is from a
client known to support Token Binding (via configuration or the
"client_access_token_token_binding_supported" metadata parameter).
7.2. Binding of Refresh Tokens
Section 6 of RFC 6749 [RFC6749] requires that a refresh token be
bound to the client to which it was issued and that, if the client
type is confidential or the client was issued client credentials (or
assigned other authentication requirements), the client must
authenticate with the authorization server when presenting the
refresh token. As a result, for non-public clients, refresh tokens
are indirectly bound to the client's credentials and cannot be used
without the associated client authentication. Non-public clients
then are afforded protections (equivalent to the strength of their
authentication credentials) against unauthorized replay of refresh
tokens and it is reasonable to not Token Bind refresh tokens for such
clients while still Toking Binding the issued access tokens. Refresh
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tokens issued to public clients, however, do not have the benefit of
such protections and authorization servers MAY elect to disallow
public clients from registering or establishing configuration that
would allow Token Bound access tokens but unbound refresh tokens.
Some web-based confidential clients implemented as distributed nodes
may be perfectly capable of implementing access token binding (if the
access token remains on the node it was bound to, the token binding
keys would be locally available for that node to prove possession),
but may struggle with refresh token binding due to an inability to
share token binding key material between nodes. As confidential
clients already have credentials which are required to use the
refresh token, and those credentials should only ever be sent over
TLS server-to-server between the client and the Token Endpoint, there
is still value in token binding access tokens without token binding
refresh tokens. Authorization servers SHOULD consider supporting
access token binding without refresh token binding for confidential
web clients as there are still security benefits to do so.
Clients MUST declare through dynamic (Section 4.1) or static
registration information what types of token bound tokens they
support to enable the server to bind tokens accordingly, taking into
account any phase-in policies. Authorization servers MAY reject
requests from any client who does not support token binding (by
returning an OAuth error response) per their own security policies.
8. IANA Considerations
8.1. 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]:
8.1.1. 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 4.1 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
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o Specification Document(s): Section 4.1 of [[ this specification ]]
8.2. OAuth Authorization Server Metadata Registration
This specification registers the following metadata definitions in
the IANA "OAuth Authorization Server Metadata" registry
[IANA.OAuth.Parameters] established by [RFC8414]:
8.2.1. 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 4.2 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 4.2 of [[ this specification ]]
8.3. PKCE Code Challenge Method Registration
This specification requests registration of the following Code
Challenge Method Parameter Names in the IANA "PKCE Code Challenge
Methods" registry [IANA.OAuth.Parameters] established by [RFC7636].
8.3.1. Registry Contents
o Code Challenge Method Parameter Name: TB-S256
o Change controller: IESG
o Specification document(s): Section 5.1.1 of [[ this specification
]]
o Code Challenge Method Parameter Name: referred_tb
o Change controller: IESG
o Specification document(s): Section 5.2.1 of [[ this specification
]]
9. Token Endpoint Authentication Method Registration
This specification requests registration of the following values in
the IANA "OAuth Token Endpoint Authentication Methods" registry
[IANA.OAuth.Parameters] established by [RFC7591].
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9.1. Registry Contents
o Token Endpoint Authentication Method Name:
"client_secret_token_bound_jwt"
o Change Controller: IESG
o Specification Document(s): Section 6 of [[ this specification ]]
o Token Endpoint Authentication Method Name:
"private_key_token_bound_jwt"
o Change Controller: IESG
o Specification Document(s): Section 6 of [[ this specification ]]
10. Sub-Namespace Registrations
This specification requests registration of the following values in
the IANA "OAuth URI" registry [IANA.OAuth.Parameters] established in
An IETF URN Sub-Namespace for OAuth [RFC6755].
10.1. Registry Contents
o URN: urn:ietf:params:oauth:grant-type:jwt-token-bound
o Common Name: Token Bound JWT Grant Type for OAuth 2.0
o Change controller: IESG
o Specification Document: Section 6 of [[ this specification ]]
o URN: urn:ietf:params:oauth:client-assertion-type:jwt-token-bound
o Common Name: Token Bound JWT for OAuth 2.0 Client Authentication
o Change controller: IESG
o Specification Document: Section 6 of [[ this specification ]]
11. References
11.1. Normative References
[IANA.OAuth.Parameters]
IANA, "OAuth Parameters",
<http://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>.
[OpenID.TokenBinding]
Jones, M., Bradley, J., and B. Campbell, "OpenID Connect
Token Bound Authentication 1.0", October 2017,
<http://openid.net/specs/
openid-connect-token-bound-authentication-1_0-03.html>.
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[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>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[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>.
[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,
<https://www.rfc-editor.org/info/rfc7230>.
[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>.
[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,
<https://www.rfc-editor.org/info/rfc7591>.
[RFC7636] Sakimura, N., Ed., Bradley, J., and N. Agarwal, "Proof Key
for Code Exchange by OAuth Public Clients", RFC 7636,
DOI 10.17487/RFC7636, September 2015,
<https://www.rfc-editor.org/info/rfc7636>.
[RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7662, DOI 10.17487/RFC7662, October 2015,
<https://www.rfc-editor.org/info/rfc7662>.
[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,
<https://www.rfc-editor.org/info/rfc7800>.
[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>.
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[RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", RFC 8414,
DOI 10.17487/RFC8414, June 2018,
<https://www.rfc-editor.org/info/rfc8414>.
[RFC8471] Popov, A., Ed., Nystroem, M., Balfanz, D., and J. Hodges,
"The Token Binding Protocol Version 1.0", RFC 8471,
DOI 10.17487/RFC8471, October 2018,
<https://www.rfc-editor.org/info/rfc8471>.
[RFC8472] Popov, A., Ed., Nystroem, M., and D. Balfanz, "Transport
Layer Security (TLS) Extension for Token Binding Protocol
Negotiation", RFC 8472, DOI 10.17487/RFC8472, October
2018, <https://www.rfc-editor.org/info/rfc8472>.
[RFC8473] Popov, A., Nystroem, M., Balfanz, D., Ed., Harper, N., and
J. Hodges, "Token Binding over HTTP", RFC 8473,
DOI 10.17487/RFC8473, October 2018,
<https://www.rfc-editor.org/info/rfc8473>.
[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>.
11.2. Informative References
[BCP212] Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps",
BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017,
<https://www.rfc-editor.org/info/rfc8252>.
[OpenID.Core]
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0", August 2015,
<http://openid.net/specs/openid-connect-core-1_0.html>.
[OpenID.Discovery]
Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
Connect Discovery 1.0", August 2015,
<http://openid.net/specs/
openid-connect-discovery-1_0.html>.
[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>.
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[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
Appendix A. Acknowledgements
This specification was developed within the OAuth Working Group under
the chairmanship of Hannes Tschofenig and Rifaat Shekh-Yusef with
Kathleen Moriarty, Eric Rescorla, and Benjamin Kaduk serving as
Security Area Directors. Additionally, the following individuals
contributed ideas, feedback, and wording that helped shape this
specification: Dirk Balfanz, Andrei Popov, Justin Richer, and Nat
Sakimura.
Appendix B. Document History
[[ to be removed by the RFC Editor before publication as an RFC ]]
-08
o Update reference to -03 of openid-connect-token-bound-
authentication.
o Update the references to the core token binding specs, which are
now RFCs 8471, 8472, and 8473.
o Update reference to AS metadata, which is now RFC 8414.
o Add chairs and ADs to the Acknowledgements.
-07
o Explicitly state that the base64url encoding of the tbh value
doesn't include any trailing pad characters, line breaks,
whitespace, etc.
o Update to latest references for tokbind drafts and draft-ietf-
oauth-discovery.
o Update reference to Implementation Considerations in draft-ietf-
tokbind-https, which is section 6 rather than 5.
o Try to tweak text that references specific sections in other
documents so that the HTML generated by the ietf tools doesn't
link to the current document (based on old suggestion from Barry
https://www.ietf.org/mail-archive/web/jose/current/msg04571.html).
-06
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o Use the boilerplate from RFC 8174.
o Update reference for draft-ietf-tokbind-https to -12 and draft-
ietf-oauth-discovery to -09.
o Minor editorial fixes.
-05
o State that authorization servers should not token bind refresh
tokens issued to a client that doesn't support bound refresh
tokens, which can be indicated by the
"client_refresh_token_token_binding_supported" client metadata
parameter.
o Add Token Binding for JWT Authorization Grants and JWT Client
Authentication.
o Adjust the language around aborting authorizations in Phasing in
Token Binding to be somewhat more general and not only about
downgrades.
o Remove reference to, and usage of, 'OAuth 2.0 Protected Resource
Metadata', which is no longer a going concern.
o Moved "Token Binding Metadata" section before "Token Binding for
Authorization Codes" to be closer to the "Token Binding for Access
Tokens" and "Token Binding for Refresh Tokens", to which it is
more closely related.
o Update references for draft-ietf-tokbind- negotiation(-10),
protocol(-16), and https(-10), as well as draft-ietf-oauth-
discovery(-07), and BCP212/RFC8252 OAuth 2.0 for Native Apps.
-04
o Define how to convey token binding information of an access token
via RFC 7662 OAuth 2.0 Token Introspection (note that the
Introspection Response Registration request for cnf/Confirmation
is in https://tools.ietf.org/html/draft-ietf-oauth-mtls-
02#section-4.3 which will likely be published and registered prior
to this document).
o Minor editorial fixes.
o Added an open issue about needing to allow for web server clients
to opt-out of having refresh tokens bound while still allowing for
binding of access tokens (following from mention of the problem on
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slide 16 of the presentation from Chicago
https://www.ietf.org/proceedings/98/slides/slides-98-oauth-sessb-
token-binding-00.pdf).
-03
o Fix a few mistakes in and around the examples that were noticed
preparing the slides for IETF 98 Chicago.
-02
o Added a section on Token Binding for authorization codes with one
variation for native clients and one for web server clients.
o Updated language to reflect that the binding is to the token
binding key pair and that proof-of-possession of that key is done
on the TLS connection.
o Added a bunch of examples.
o Added a few Open Issues so they are tracked in the document.
o Updated the Token Binding and OAuth Metadata references.
o Added William Denniss as an author.
-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".
-00
o Created the initial working group version from draft-jones-oauth-
token-binding-00.
Authors' Addresses
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Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: http://self-issued.info/
Brian Campbell
Ping Identity
Email: brian.d.campbell@gmail.com
John Bradley
Yubico
Email: ve7jtb@ve7jtb.com
URI: http://www.thread-safe.com/
William Denniss
Google
1600 Amphitheatre Pkwy
Mountain View, CA 94043
USA
Email: wdenniss@google.com
URI: http://wdenniss.com/
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