draft-ietf-tokbind-https-07.txt   draft-ietf-tokbind-https-08.txt 
Internet Engineering Task Force A. Popov Internet Engineering Task Force A. Popov
Internet-Draft M. Nystroem Internet-Draft M. Nystroem
Intended status: Standards Track Microsoft Corp. Intended status: Standards Track Microsoft Corp.
Expires: May 27, 2017 D. Balfanz, Ed. Expires: August 20, 2017 D. Balfanz, Ed.
A. Langley A. Langley
Google Inc. Google Inc.
J. Hodges J. Hodges
Paypal Paypal
November 23, 2016 February 16, 2017
Token Binding over HTTP Token Binding over HTTP
draft-ietf-tokbind-https-07 draft-ietf-tokbind-https-08
Abstract Abstract
This document describes a collection of mechanisms that allow HTTP This document describes a collection of mechanisms that allow HTTP
servers to cryptographically bind authentication tokens (such as servers to cryptographically bind security tokens (such as cookies
cookies and OAuth tokens) to TLS [RFC5246] connections. and OAuth tokens) to TLS [RFC5246] connections.
We describe both _first-party_ and _federated_ scenarios. In a We describe both _first-party_ and _federated_ scenarios. In a
first-party scenario, an HTTP server is able to cryptographically first-party scenario, an HTTP server is able to cryptographically
bind the security tokens it issues to a client, and which the client bind the security tokens it issues to a client, and which the client
subsequently returns to the server, to the TLS connection between the subsequently returns to the server, to the TLS connection between the
client and server. Such bound security tokens are protected from client and server. Such bound security tokens are protected from
misuse since the server can generally detect if they are replayed misuse since the server can generally detect if they are replayed
inappropriately, e.g., over other TLS connections. inappropriately, e.g., over other TLS connections.
Federated token bindings, on the other hand, allow servers to Federated token bindings, on the other hand, allow servers to
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 27, 2017. This Internet-Draft will expire on August 20, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. The Sec-Token-Binding Header Field . . . . . . . . . . . . . 4 2. The Sec-Token-Binding HTTP Request Header Field . . . . . . . 4
2.1. HTTPS Token Binding Key Pair Scoping . . . . . . . . . . 5 2.1. HTTPS Token Binding Key Pair Scoping . . . . . . . . . . 5
3. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . . . 5 3. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . . . 6
4. First-party Use Cases . . . . . . . . . . . . . . . . . . . . 6 4. First-party Use Cases . . . . . . . . . . . . . . . . . . . . 6
5. Federation Use Cases . . . . . . . . . . . . . . . . . . . . 6 5. Federation Use Cases . . . . . . . . . . . . . . . . . . . . 6
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 6 5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. HTTP Redirects . . . . . . . . . . . . . . . . . . . . . 8 5.3. HTTP Redirects . . . . . . . . . . . . . . . . . . . . . 8
5.4. Negotiated Key Parameters . . . . . . . . . . . . . . . . 10 5.4. Negotiated Key Parameters . . . . . . . . . . . . . . . . 10
5.5. Federation Example . . . . . . . . . . . . . . . . . . . 10 5.5. Federation Example . . . . . . . . . . . . . . . . . . . 11
6. Implementation Considerations . . . . . . . . . . . . . . . . 13 6. Implementation Considerations . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7.1. Security Token Replay . . . . . . . . . . . . . . . . . . 13 7.1. Security Token Replay . . . . . . . . . . . . . . . . . . 13
7.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS 7.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS
Versions . . . . . . . . . . . . . . . . . . . . . . . . 13 Versions . . . . . . . . . . . . . . . . . . . . . . . . 14
7.3. Sensitivity of the Sec-Token-Binding Header . . . . . . . 14 7.3. Sensitivity of the Sec-Token-Binding Header . . . . . . . 14
7.4. Securing Federated Sign-On Protocols . . . . . . . . . . 15 7.4. Securing Federated Sign-On Protocols . . . . . . . . . . 15
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 17 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 17
8.1. Scoping of Token Binding Keys . . . . . . . . . . . . . . 17 8.1. Scoping of Token Binding Key Pairs . . . . . . . . . . . 17
8.2. Life Time of Token Binding Keys . . . . . . . . . . . . . 17 8.2. Life Time of Token Binding Key Pairs . . . . . . . . . . 18
8.3. Correlation . . . . . . . . . . . . . . . . . . . . . . . 18 8.3. Correlation . . . . . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 19 11.1. Normative References . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 20 11.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
The Token Binding Protocol [I-D.ietf-tokbind-protocol] defines a The Token Binding Protocol [I-D.ietf-tokbind-protocol] defines a
Token Binding ID for a TLS connection between a client and a server. Token Binding ID for a TLS connection between a client and a server.
The Token Binding ID of a TLS connection is related to a private key, The Token Binding ID of a TLS connection is constructed using the
that the client proves possession of to the server, and is long-lived public key of a private-public key pair. The client proves
(i.e., subsequent TLS connections between the same client and server possession of the corresponding private key. This Token Binding key
have the same Token Binding ID). When issuing a security token (e.g. pair is long-lived (i.e., subsequent TLS connections between the same
an HTTP cookie or an OAuth token) to a client, the server can include client and server have the same Token Binding ID, unless specifically
reset, e.g., by the user). When issuing a security token (e.g. an
HTTP cookie or an OAuth token) to a client, the server can include
the Token Binding ID in the token, thus cryptographically binding the the Token Binding ID in the token, thus cryptographically binding the
token to TLS connections between that particular client and server, token to TLS connections between that particular client and server,
and inoculating the token against abuse (re-use, attempted and inoculating the token against abuse (re-use, attempted
impersonation, etc.) by attackers. impersonation, etc.) by attackers.
While the Token Binding Protocol [I-D.ietf-tokbind-protocol] defines While the Token Binding Protocol [I-D.ietf-tokbind-protocol] defines
a message format for establishing a Token Binding ID, it does not a message format for establishing a Token Binding ID, it does not
specify how this message is embedded in higher-level protocols. The specify how this message is embedded in higher-level protocols. The
purpose of this specification is to define how TokenBindingMessages purpose of this specification is to define how TokenBindingMessages
are embedded in HTTP (both versions 1.1 [RFC7230] and 2 [RFC7540]). are embedded in HTTP (both versions 1.1 [RFC7230] and 2 [RFC7540]).
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Token Binding ID that the client is using with a _different_ server Token Binding ID that the client is using with a _different_ server
than the one that the TokenBindingMessage is sent to. This is useful than the one that the TokenBindingMessage is sent to. This is useful
in federation scenarios. in federation scenarios.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. The Sec-Token-Binding Header Field 2. The Sec-Token-Binding HTTP Request Header Field
Once a client and server have negotiated the Token Binding Protocol Once a client and server have negotiated the Token Binding Protocol
with HTTP/1.1 or HTTP/2 (see [I-D.ietf-tokbind-protocol] and with HTTP/1.1 or HTTP/2 (see [I-D.ietf-tokbind-protocol] and
[I-D.ietf-tokbind-negotiation]), clients MUST include the Sec-Token- [I-D.ietf-tokbind-negotiation]), clients MUST include a Sec-Token-
Binding header field in their HTTP requests. The ABNF of the Sec- Binding header field in their HTTP requests, and MUST include only
Token-Binding header field is (in [RFC7230] style, see also [RFC7231] one such header field per HTTP request. Also, The Sec-Token-Binding
Section 8.3): header field MUST NOT be included in HTTP responses. The ABNF of the
Sec-Token-Binding header field is (in [RFC7230] style, see also
[RFC7231] Section 8.3):
Sec-Token-Binding = EncodedTokenBindingMessage Sec-Token-Binding = EncodedTokenBindingMessage
The header field name is "Sec-Token-Binding" and its value is a The header field name is "Sec-Token-Binding" and its single value,
base64url encoding of the TokenBindingMessage defined in EncodedTokenBindingMessage, is a base64url encoding of a single
[I-D.ietf-tokbind-protocol] using the URL- and filename-safe TokenBindingMessage, as defined in [I-D.ietf-tokbind-protocol], using
character set described in Section 5 of [RFC4648], with all trailing the URL- and filename-safe character set described in Section 5 of
pad characters '=' omitted and without the inclusion of any line [RFC4648], with all trailing pad characters '=' omitted and without
breaks, whitespace, or other additional characters. the inclusion of any line breaks, whitespace, or other additional
characters.
For example: For example:
Sec-Token-Binding: <base64url-encoded TokenBindingMessage> Sec-Token-Binding: <base64url-encoded TokenBindingMessage>
If the server receives more than one Sec-Token-Binding header field
in an HTTP request, then the server MUST reject the message with a
400 (Bad Request) HTTP status code. Additionally, the Sec-Token-
Binding header field:
SHOULD NOT be stored by origin servers on PUT requests,
MAY be listed by a server in a Vary response header field, and,
MUST NOT be used in HTTP trailers.
The TokenBindingMessage MUST contain one TokenBinding structure with The TokenBindingMessage MUST contain one TokenBinding structure with
TokenBindingType of provided_token_binding, which MUST be signed with TokenBindingType of provided_token_binding, which MUST be signed with
the Token Binding private key used by the client for connections the Token Binding private key used by the client for connections
between itself and the server that the HTTP request is sent to between itself and the server that the HTTP request is sent to
(clients use different Token Binding keys for different servers, see (clients use different Token Binding key pairs for different servers,
Section 2.1 below). The Token Binding ID established by this see Section 2.1 below). The Token Binding ID established by this
TokenBinding is called a _Provided Token Binding ID_. TokenBinding is called a _Provided Token Binding ID_.
The TokenBindingMessage MAY also contain one TokenBinding structure The TokenBindingMessage MAY also contain one TokenBinding structure
with TokenBindingType of referred_token_binding, as specified in with TokenBindingType of referred_token_binding, as specified in
Section 5.3. In addition to the latter, or rather than the latter, Section 5.3. In addition to the latter, or rather than the latter,
the TokenBindingMessage MAY contain other TokenBinding structures. the TokenBindingMessage MAY contain other TokenBinding structures.
This is use case-specific, and such use cases are outside the scope This is use case-specific, and such use cases are outside the scope
of this specification. of this specification.
A TokenBindingMessage is validated by the server as described in A TokenBindingMessage is validated by the server as described in
Section 4.2. "Server Processing Rules" of Section 4.2. "Server Processing Rules" of
[I-D.ietf-tokbind-protocol]. If validaion fails and a Token Binding [I-D.ietf-tokbind-protocol]. If validation fails and a Token Binding
is rejected, any associated bound tokens MUST also be rejected by the is rejected, any associated bound tokens MUST also be rejected by the
server. HTTP requests containing invalid tokens MUST be rejected. server. HTTP requests containing invalid tokens MUST be rejected.
In this case, the server application may return HTTP status code 400 In this case, the server application MAY return HTTP status code 400
(Bad Request) or proceed with an application-specific invalid token (Bad Request) or proceed with an application-specific invalid token
response (e.g. directing the client to re-authenticate and present a response (e.g. directing the client to re-authenticate and present a
different token), or terminate the connection. different token), or terminate the connection.
In HTTP/2, the client SHOULD use Header Compression [RFC7541] to In HTTP/2, the client SHOULD use Header Compression [RFC7541] to
avoid the overhead of repeating the same header field in subsequent avoid the overhead of repeating the same header field in subsequent
HTTP requests. HTTP requests.
2.1. HTTPS Token Binding Key Pair Scoping 2.1. HTTPS Token Binding Key Pair Scoping
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latter context, HTTP cookies [RFC6265] are typically utilized for latter context, HTTP cookies [RFC6265] are typically utilized for
state management, including client authentication. A related, though state management, including client authentication. A related, though
distinct, example of other HTTP-based application contexts is where distinct, example of other HTTP-based application contexts is where
OAuth tokens [RFC6749] are utilized to manage authorization for OAuth tokens [RFC6749] are utilized to manage authorization for
third-party application access to resources. The token scoping rules third-party application access to resources. The token scoping rules
of these two examples can differ: the scoping rules for cookies are of these two examples can differ: the scoping rules for cookies are
concisely specified in [RFC6265], whereas OAuth is a framework and concisely specified in [RFC6265], whereas OAuth is a framework and
defines various token types with various scopings, some of which are defines various token types with various scopings, some of which are
determined by the encompassing application. determined by the encompassing application.
The Token Binding key pair scoping for those key pairs generated by The scoping for those Token Binding key pairs generated by Web
Web browsers in the context of the first-party and federation use browsers in the context of the first-party and federation use cases
cases defined in this specification (below), and to be used for defined in this specification (below), and to be used for binding
binding HTTP cookies MUST be at the granularity of "effective top- HTTP cookies MUST be at the granularity of "effective top-level
level domain (public suffix) + 1" (eTLD+1), i.e., at the same domain (public suffix) + 1" (eTLD+1), i.e., at the same granularity
granularity at which cookies can be set (see [RFC6265]). Key pairs at which cookies can be set (see [RFC6265]). Key pairs used to bind
used to bind other application tokens, such as OAuth tokens or Open other application tokens, such as OAuth tokens or Open ID Connect "ID
ID Connect "ID Tokens", SHOULD generally adhere to the above eTLD+1 Tokens", SHOULD generally adhere to the above eTLD+1 scoping
scoping requirement for those tokens being employed in first-party or requirement for those tokens being employed in first-party or
federation scenarios as described below. Applications other than Web federation scenarios as described below. Applications other than Web
browsers MAY use different key scoping rules. See also Section 8.1, browsers MAY use different key pair scoping rules. See also
below. Section 8.1, below.
Scoping rules for other HTTP-based application contexts are outside Scoping rules for other HTTP-based application contexts are outside
the scope of this specification. the scope of this specification.
3. TLS Renegotiation 3. TLS Renegotiation
Token Binding over HTTP/1.1 [RFC7230] can be performed in combination Token Binding over HTTP/1.1 [RFC7230] can be performed in combination
with TLS renegotiation. In this case, renegotiation MUST only occur with TLS renegotiation. In this case, renegotiation MUST only occur
between a client's HTTP request and the server's response, the client between a client's HTTP request and the server's response, the client
MUST NOT send any pipelined requests, and the client MUST NOT MUST NOT send any pipelined requests, and the client MUST NOT
initiate renegotiation (i.e. the client may only send a renegotiation initiate renegotiation (i.e., the client may only send a
ClientHello in response to the server's HelloRequest). These renegotiation ClientHello in response to the server's HelloRequest).
conditions ensure that both the client and the server can clearly These conditions ensure that both the client and the server can
identify which TLS Exported Keying Material value [RFC5705] to use clearly identify which TLS Exported Keying Material value [RFC5705]
when generating or verifying the TokenBindingMessage. This also to use when generating or verifying the TokenBindingMessage. This
prevents a TokenBindingMessage from being split across TLS also prevents a TokenBindingMessage from being split across TLS
renegotiation(s). renegotiation boundaries (i.e., due to TLS message fragmentation -
see Section 6.2.1 of [RFC5246]).
4. First-party Use Cases 4. First-party Use Cases
In a first-party use case, an HTTP server issues a security token In a first-party use case (also known as a "same-site" use case), an
such as a cookie (or similar) to a client, and expects the client to HTTP server issues a security token such as a cookie (or similar) to
return the security token at a later time, e.g., in order to a client, and expects the client to return the security token at a
authenticate. Binding the security token to the TLS connection later time, e.g., in order to authenticate. Binding the security
between client and server protects the security token from misuse token to the TLS connection between client and server protects the
since the server can detect if the security token is replayed security token from misuse since the server can detect if the
inappropriately, e.g., over other TLS connections. security token is replayed inappropriately, e.g., over other TLS
connections.
See [I-D.ietf-tokbind-protocol] Section 6 for general guidance See [I-D.ietf-tokbind-protocol] Section 5 for general guidance
regarding binding of security tokens and their subsequent validation. regarding binding of security tokens and their subsequent validation.
5. Federation Use Cases 5. Federation Use Cases
5.1. Introduction 5.1. Introduction
For privacy reasons, clients use different private keys to establish For privacy reasons, clients use different Token Binding key pairs to
Provided Token Binding IDs with different servers. As a result, a establish Provided Token Binding IDs with different servers. As a
server cannot bind a security token (such as an OAuth token or an result, a server cannot bind a security token (such as an OAuth token
OpenID Connect identity token) to a TLS connection that the client or an OpenID Connect identity token) to a TLS connection that the
has with a different server. This is, however, a common requirement client has with a different server. This is, however, a common
in federation scenarios: For example, an Identity Provider may wish requirement in federation scenarios: For example, an Identity
to issue an identity token to a client and cryptographically bind Provider may wish to issue an identity token to a client and
that token to the TLS connection between the client and a Relying cryptographically bind that token to the TLS connection between the
Party. client and a Relying Party.
In this section we describe mechanisms to achieve this. The common In this section we describe mechanisms to achieve this. The common
idea among these mechanisms is that a server (called the _Token idea among these mechanisms is that a server (called the _Token
Consumer_ in this document) signals to the client that it should Consumer_ in this document) signals to the client that it should
reveal the Provided Token Binding ID that is used between the client reveal the Provided Token Binding ID that is used between the client
and itself, to another server (called the _Token Provider_ in this and itself, to another server (called the _Token Provider_ in this
document). Also common across the mechanisms is how the Token document). Also common across the mechanisms is how the Token
Binding ID is revealed to the Token Provider: The client uses the Binding ID is revealed to the Token Provider: The client uses the
Token Binding Protocol [I-D.ietf-tokbind-protocol], and includes a Token Binding Protocol [I-D.ietf-tokbind-protocol], and includes a
TokenBinding structure in the Sec-Token-Binding HTTP header field TokenBinding structure in the Sec-Token-Binding HTTP header field
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o The client delivers the token request to the Token Provider. o The client delivers the token request to the Token Provider.
o The Token Provider issues the token. The token is issued for the o The Token Provider issues the token. The token is issued for the
specific Token Consumer who requested it (thus preventing specific Token Consumer who requested it (thus preventing
malicious Token Consumers from using tokens with other Token malicious Token Consumers from using tokens with other Token
Consumers). The token is, however, typically a bearer token, Consumers). The token is, however, typically a bearer token,
meaning that any client can use it with the Token Consumer, not meaning that any client can use it with the Token Consumer, not
just the client to which it was issued. just the client to which it was issued.
o Therefore, in the previous step, the Token Provider may want to o Therefore, in the previous step, the Token Provider may want to
include in the token the Token-Binding public key that the client include in the token the Token Binding ID that the client uses
uses when communicating with the Token Consumer, thus _binding_ when communicating with the Token Consumer, thus _binding_ the
the token to client's Token-Binding keypair. The client proves token to the client's Token Binding key pair. The client proves
possession of the private key when communicating with the Token possession of the private key when communicating with the Token
Consumer through the Token Binding Protocol Consumer through the Token Binding Protocol
[I-D.ietf-tokbind-protocol], and reveals the corresponding public [I-D.ietf-tokbind-protocol], and reveals the corresponding public
key of this keypair as part of the Token Binding ID. Comparing key of this key pair as part of the Token Binding ID. Comparing
the public key from the token with the public key from the Token the Token Binding ID from the token to the Token Binding ID
Binding ID allows the Token Consumer to verify that the token was established with the client allows the Token Consumer to verify
sent to it by the legitimate client. that the token was sent to it by the legitimate client.
o To allow the Token Provider to include the Token-Binding public o To allow the Token Provider to include the Token Binding ID in the
key in the token, the Token Binding ID (between client and Token token, the Token Binding ID (between client and Token Consumer)
Consumer) must therefore be communicated to the Token Provider must therefore be communicated to the Token Provider along with
along with the token request. Communicating a Token Binding ID the token request. Communicating a Token Binding ID involves
involves proving possession of a private key and is described in proving possession of a private key and is described in the Token
the Token Binding Protocol [I-D.ietf-tokbind-protocol]. Binding Protocol [I-D.ietf-tokbind-protocol].
The client will perform this last operation (proving possession of a The client will perform this last operation (proving possession of a
private key that corresponds to a Token Binding ID between the client private key that corresponds to a Token Binding ID between the client
and the Token Consumer while delivering the token request to the and the Token Consumer while delivering the token request to the
Token Provider) only if the Token Consumer requests the client to do Token Provider) only if the Token Consumer requests the client to do
so. so.
Below, we specify how Token Consumers can signal this request in Below, we specify how Token Consumers can signal this request in
redirect-based federation protocols. Note that this assumes that the redirect-based federation protocols. Note that this assumes that the
federated sign-on flow starts at the Token Consumer, or at the very federated sign-on flow starts at the Token Consumer, or at the very
least include a redirect from Token Consumer to Token Provider. It least includes a redirect from Token Consumer to Token Provider. It
is outside the scope of this document to specify similar mechanisms is outside the scope of this document to specify similar mechanisms
for flows that do not include such redirects. for flows that do not include such redirects.
5.3. HTTP Redirects 5.3. HTTP Redirects
When a Token Consumer redirects the client to a Token Provider as a When a Token Consumer redirects the client to a Token Provider as a
means to deliver the token request, it SHOULD include a Include- means to deliver the token request, it SHOULD include a Include-
Referred-Token-Binding-ID HTTP response header field in its HTTP Referred-Token-Binding-ID HTTP response header field in its HTTP
response. The ABNF of the Include-Referred-Token-Binding-ID header response. The ABNF of the Include-Referred-Token-Binding-ID header
is (in [RFC7230] style, see also [RFC7231] Section 8.3): is (in [RFC7230] style, see also [RFC7231] Section 8.3):
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This header field has only meaning if the HTTP status code is 301, This header field has only meaning if the HTTP status code is 301,
302, 303, 307 or 308, and MUST be ignored by the client for any other 302, 303, 307 or 308, and MUST be ignored by the client for any other
status codes. If the client supports the Token Binding Protocol, and status codes. If the client supports the Token Binding Protocol, and
has negotiated the Token Binding Protocol with both the Token has negotiated the Token Binding Protocol with both the Token
Consumer and the Token Provider, it already sends the Sec-Token- Consumer and the Token Provider, it already sends the Sec-Token-
Binding header field to the Token Provider with each HTTP request Binding header field to the Token Provider with each HTTP request
(see above). (see above).
The TokenBindingMessage SHOULD contain a TokenBinding with The TokenBindingMessage SHOULD contain a TokenBinding with
TokenBindingType referred_token_binding. If included, this TokenBindingType referred_token_binding. If included, this
TokenBinding MUST be signed with the Token Binding key used by the TokenBinding MUST be signed with the Token Binding private key used
client for connections between itself and the Token Consumer (more by the client for connections between itself and the Token Consumer
specifically, the web origin that issued the Include-Referred-Token- (more specifically, the server that issued the Include-Referred-
Binding-ID response header field). The Token Binding ID established Token-Binding-ID response header field). The Token Binding ID
by this TokenBinding is called a _Referred Token Binding ID_. established by this TokenBinding is called a _Referred Token Binding
ID_.
As described above, the TokenBindingMessage MUST additionally contain As described above, the TokenBindingMessage MUST additionally contain
a Provided Token Binding ID, i.e., a TokenBinding structure with a Provided Token Binding ID, i.e., a TokenBinding structure with
TokenBindingType provided_token_binding, which MUST be signed with TokenBindingType of provided_token_binding, which MUST be signed with
the Token Binding key used by the client for connections between the Token Binding private key used by the client for connections
itself and the Token Provider (more specifically, the web origin that between itself and the Token Provider (more specifically, the server
the token request is being sent to). that the token request is being sent to).
If for some deployment-specific reason the initial Token Provider If for some deployment-specific reason the initial Token Provider
("TP1") needs to redirect the client to another Token Provider ("TP1") needs to redirect the client to another Token Provider
("TP2"), rather than directly back to the Token Consumer, it can be ("TP2"), rather than directly back to the Token Consumer, it can be
accomodated using the header fields defined in this specification in accommodated using the header fields defined in this specification in
the following fashion ("the redirect-chain approach"): the following fashion ("the redirect-chain approach"):
Initially, the client is redirected to TP1 by the Token Consumer Initially, the client is redirected to TP1 by the Token Consumer
("TC"), as described above. Upon receiving the client's request, ("TC"), as described above. Upon receiving the client's request,
containing a TokenBindingMessage which contains both provided and containing a TokenBindingMessage which contains both provided and
referred TokenBindings (for TP1 and TC, respectively), TP1 referred TokenBindings (for TP1 and TC, respectively), TP1
responds to the client with a redirect response containing the responds to the client with a redirect response containing the
Include-Referred-Token-Binding-ID header field and directing the Include-Referred-Token-Binding-ID header field and directing the
client to send a request to TP2. This causes the client to follow client to send a request to TP2. This causes the client to follow
the same pattern and send a request containing a the same pattern and send a request containing a
skipping to change at page 10, line 17 skipping to change at page 10, line 41
The above is intended as only a non-normative example. Details are The above is intended as only a non-normative example. Details are
specific to deployment contexts. Other approaches are possible, but specific to deployment contexts. Other approaches are possible, but
are outside the scope of this specification. are outside the scope of this specification.
5.4. Negotiated Key Parameters 5.4. Negotiated Key Parameters
The TLS Extension for Token Binding Protocol Negotiation The TLS Extension for Token Binding Protocol Negotiation
[I-D.ietf-tokbind-negotiation] allows the server and client to [I-D.ietf-tokbind-negotiation] allows the server and client to
negotiate the parameters (signature algorithm, length) of the Token negotiate the parameters (signature algorithm, length) of the Token
Binding key. It is possible that the Token Binding ID used between Binding key pair. It is possible that the Token Binding ID used
the client and the Token Consumer, and the Token Binding ID used between the client and the Token Consumer, and the Token Binding ID
between the client and Token Provider, use different key parameters. used between the client and Token Provider, use different key
The client MUST use the key parameters negotiated with the Token parameters. The client MUST use the key parameters negotiated with
Consumer in the referred_token_binding TokenBinding of the the Token Consumer in the referred_token_binding TokenBinding of the
TokenBindingMessage, even if those key parameters are different from TokenBindingMessage, even if those key parameters are different from
the ones negotiated with the origin that the header field is sent to. the ones negotiated with the server that the header field is sent to.
Token Providers SHOULD support all the Token Binding key parameters Token Providers SHOULD support all the Token Binding key parameters
specified in the [I-D.ietf-tokbind-protocol]. If a token provider specified in [I-D.ietf-tokbind-protocol]. If a token provider does
does not support the key parameters specified in the not support the key parameters specified in the
referred_token_binding TokenBinding in the TokenBindingMessage, it referred_token_binding TokenBinding in the TokenBindingMessage, it
MUST NOT issue a bound token. MUST NOT issue a bound token.
5.5. Federation Example 5.5. Federation Example
The diagram below shows a typical HTTP Redirect-based Web Browser SSO The diagram below shows a typical HTTP Redirect-based Web Browser SSO
Profile (no artifact, no callbacks), featuring binding of, e.g., a Profile (no artifact, no callbacks), featuring binding of, e.g., a
TLS Token Binding ID into an OpenID Connect "ID Token". TLS Token Binding ID into an OpenID Connect "ID Token".
Legend: Legend:
skipping to change at page 12, line 41 skipping to change at page 12, line 50
| | | | | |
| 3a. ID Token containing Kp1, issued for TC, | | 3a. ID Token containing Kp1, issued for TC, |
| conveyed via OIDC "Authentication Response" | | conveyed via OIDC "Authentication Response" |
+<- - - - - - - - - - - - - - - - - - - - - - - - - - - -| +<- - - - - - - - - - - - - - - - - - - - - - - - - - - -|
. | (redirect to TC) | | . | (redirect to TC) | |
. | | | . | | |
. | | | . | | |
+-------------------------------->| | +-------------------------------->| |
| 3b. HTTPS GET or POST with | | 3b. HTTPS GET or POST with |
| ETBMSG[[{EKM1}Ks1,TBID1,provided_token_binding]] | | ETBMSG[[{EKM1}Ks1,TBID1,provided_token_binding]] |
| conveying Authn Reponse containing | | conveying Authn Response containing |
| ID Token w/TBID1, issued for TC | | ID Token w/TBID1, issued for TC |
| | | | | |
| | | | | |
| | | | | |
| 4. user is signed-on, any security-relevant cookie(s)| | 4. user is signed-on, any security-relevant cookie(s)|
| that are set SHOULD contain TBID1 | | that are set SHOULD contain TBID1 |
|<------------------------------| | |<------------------------------| |
| | | | | |
| | | | | |
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Binding messages, containing Token Binding IDs of various Binding messages, containing Token Binding IDs of various
application-specified Token Binding types and for application- application-specified Token Binding types and for application-
specified TLS connections, conveyed over an application-specified specified TLS connections, conveyed over an application-specified
HTTPS connection, i.e., within the TokenBindingMessage conveyed by HTTPS connection, i.e., within the TokenBindingMessage conveyed by
the Sec-Token-Binding header field. the Sec-Token-Binding header field.
However, such implementations MUST only convey Token Binding IDs to However, such implementations MUST only convey Token Binding IDs to
servers if signaled to do so by an application. For example, a servers if signaled to do so by an application. For example, a
server can return an Include-Referred-Token-Binding-ID HTTP response server can return an Include-Referred-Token-Binding-ID HTTP response
header field to a Web browser, thus signaling to the Token Binding header field to a Web browser, thus signaling to the Token Binding
implementation in the Web browser that the Web application associated implementation in the Web browser that the server intends to convey
with the server's origin intents to convey the Web browser's Token the Web browser's Token Binding ID to another server. Other
Binding ID to another server. Other signaling mechanisms are signaling mechanisms are possible, and are specific to the
possible, but are outside the scope of this specification. application layer protocol, but are outside the scope of this
specification.
NOTE: See Section 8 "Privacy Considerations", for privacy guidance NOTE: See Section 8 "Privacy Considerations", for privacy guidance
regarding the use of this functionality. regarding the use of this functionality.
7. Security Considerations 7. Security Considerations
7.1. Security Token Replay 7.1. Security Token Replay
The goal of the Federated Token Binding mechanisms is to prevent The goal of the Federated Token Binding mechanisms is to prevent
attackers from exporting and replaying tokens used in protocols attackers from exporting and replaying tokens used in protocols
between the client and Token Consumer, thereby impersonating between the client and Token Consumer, thereby impersonating
legitimate users and gaining access to protected resources. Bound legitimate users and gaining access to protected resources. Although
tokens can still be replayed by malware present in the client. In bound tokens can still be replayed by any malware present in clients
order to export the token to another machine and successfully replay (which may be undetectable by a server), in order to export bound
it, the attacker also needs to export the corresponding private key. tokens to other machines and successfully replay them, attackers also
The Token Binding private key is therefore a high-value asset and need to export the corresponding Token Binding private keys. Token
MUST be strongly protected, ideally by generating it in a hardware Binding private keys are therefore high-value assets and SHOULD be
security module that prevents key export. strongly protected, ideally by generating them in a hardware security
module that prevents key export.
7.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS Versions 7.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS Versions
The Token Binding protocol relies on the exported key material (EKM) The Token Binding protocol relies on the exported key material (EKM)
value [RFC5705] to associate a TLS connection with a TLS Token value [RFC5705] to associate a TLS connection with a TLS Token
Binding. The triple handshake attack [TRIPLE-HS] is a known Binding. The triple handshake attack [TRIPLE-HS] is a known
vulnerability in TLS 1.2 and older TLS versions, allowing the vulnerability in TLS 1.2 and older TLS versions, allowing the
attacker to synchronize keying material between TLS connections. The attacker to synchronize keying material between TLS connections. The
attacker can then successfully replay bound tokens. For this reason, attacker can then successfully replay bound tokens. For this reason,
the Token Binding protocol MUST NOT be negotiated with these TLS the Token Binding protocol MUST NOT be negotiated with these TLS
skipping to change at page 14, line 19 skipping to change at page 14, line 30
negotiated. negotiated.
7.3. Sensitivity of the Sec-Token-Binding Header 7.3. Sensitivity of the Sec-Token-Binding Header
The purpose of the Token Binding protocol is to convince the server The purpose of the Token Binding protocol is to convince the server
that the client that initiated the TLS connection controls a certain that the client that initiated the TLS connection controls a certain
key pair. For the server to correctly draw this conclusion after key pair. For the server to correctly draw this conclusion after
processing the Sec-Token-Binding header field, certain secrecy and processing the Sec-Token-Binding header field, certain secrecy and
integrity requirements must be met. integrity requirements must be met.
For example, the client's private Token Binding key must be kept For example, the client's Token Binding private key must be kept
secret by the client. If the private key is not secret, then another secret by the client. If the private key is not secret, then another
actor in the system could create a valid Token Binding header field, actor in the system could create a valid Token Binding header field,
impersonating the client. This can render the main purpose of the impersonating the client. This can render the main purpose of the
protocol - to bind bearer tokens to certain clients - moot: Consider, protocol - to bind bearer tokens to certain clients - moot: Consider,
for example, an attacker who obtained (perhaps through a network for example, an attacker who obtained (perhaps through a network
intrusion) an authentication cookie that a client uses with a certain intrusion) an authentication cookie that a client uses with a certain
server. Consider further that the server bound that cookie to the server. Consider further that the server bound that cookie to the
client's Token Binding ID precisely to thwart misuse of the cookie. client's Token Binding ID precisely to thwart misuse of the cookie.
If the attacker were to come into possession of the client's private If the attacker were to come into possession of the client's private
key, he could then establish a TLS connection with the server and key, he could then establish a TLS connection with the server and
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EKM to recover the TLS master secret. Such considerations might lead EKM to recover the TLS master secret. Such considerations might lead
some clients to not treat the EKM as a secret.) Such an attacker A some clients to not treat the EKM as a secret.) Such an attacker A
could craft a Sec-Token-Binding header field with A's key pair over could craft a Sec-Token-Binding header field with A's key pair over
C's EKM. If the attacker could now trick C to send such a header C's EKM. If the attacker could now trick C to send such a header
field to S, it would appear to S as if C controls a certain key pair field to S, it would appear to S as if C controls a certain key pair
when in fact it does not (the attacker A controls the key pair). when in fact it does not (the attacker A controls the key pair).
If A has a pre-existing relationship with S (perhaps has an account If A has a pre-existing relationship with S (perhaps has an account
on S), it now appears to the server S as if A is connecting to it, on S), it now appears to the server S as if A is connecting to it,
even though it is really C. (If the server S does not simply use even though it is really C. (If the server S does not simply use
Token Binding keys to identify clients, but also uses bound Token Binding IDs to identify clients, but also uses bound
authentication cookies, then A would also have to trick C into authentication cookies, then A would also have to trick C into
sending one of A's cookies to S, which it can do through a variety of sending one of A's cookies to S, which it can do through a variety of
means - inserting cookies through Javascript APIs, setting cookies means - inserting cookies through Javascript APIs, setting cookies
through related-domain attacks, etc.) In other words, A tricked C through related-domain attacks, etc.) In other words, A tricked C
into logging into A's account on S. This could lead to a loss of into logging into A's account on S. This could lead to a loss of
privacy for C, since A presumably has some other way to also access privacy for C, since A presumably has some other way to also access
the account, and can thus indirectly observe A's behavior (for the account, and can thus indirectly observe A's behavior (for
example, if S has a feature that lets account holders see their example, if S has a feature that lets account holders see their
activity history on S). activity history on S).
Therefore, we need to protect the integrity of the Sec-Token-Binding Therefore, we need to protect the integrity of the Sec-Token-Binding
header field. One origin should not be able to set the Sec-Token- header field. One eTLD+1 should not be able to set the Sec-Token-
Binding header field (through a DOM API or otherwise) that the User Binding header field (through a DOM API or otherwise) that the User
Agent uses with another origin. Employing the "Sec-" header field Agent uses with another eTLD+1. Employing the "Sec-" header field
prefix helps to meet this requirement by denoting the header field prefix helps to meet this requirement by denoting the header field
name to be a "forbidden header name", see [fetch-spec]. name to be a "forbidden header name", see [fetch-spec].
7.4. Securing Federated Sign-On Protocols 7.4. Securing Federated Sign-On Protocols
As explained above, in a federated sign-in scenario a client will As explained above, in a federated sign-in scenario a client will
prove possession of two different key pairs to a Token Provider: One prove possession of two different Token Binding private keys to a
key pair is the "provided" Token Binding key pair (which the client Token Provider: One private key corresponds to the "provided" Token
normally uses with the Token Provider), and the other is the Binding ID (which the client normally uses with the Token Provider),
"referred" Token Binding key pair (which the client normally uses and the other is the Token Binding private key corresponding to the
with the Token Consumer). The Token Provider is expected to issue a "referred" Token Binding ID (which the client normally uses with the
token that is bound to the referred Token Binding key. Token Consumer). The Token Provider is expected to issue a token
that is bound to the referred Token Binding ID.
Both proofs (that of the provided Token Binding key and that of the Both proofs (that of the provided Token Binding private key and that
referred Token Binding key) are necessary. To show this, consider of the referred Token Binding private key) are necessary. To show
the following scenario: this, consider the following scenario:
o The client has an authentication token with the Token Provider o The client has an authentication token with the Token Provider
that is bound to the client's Token Binding key. that is bound to the client's Token Binding ID used with that
Token Provider.
o The client wants to establish a secure (i.e., free of men-in-the- o The client wants to establish a secure (i.e., free of men-in-the-
middle) authenticated session with the Token Consumer, but has not middle) authenticated session with the Token Consumer, but has not
done so yet (in other words, we are about to run the federated done so yet (in other words, we are about to run the federated
sign-on protocol). sign-on protocol).
o A man-in-the-middle is allowed to intercept the connection between o A man-in-the-middle is allowed to intercept the connection between
client and Token Consumer or between Client and Token Provider (or client and Token Consumer or between Client and Token Provider (or
both). both).
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scenarios. scenarios.
First, consider a man-in-the-middle between the client and the Token First, consider a man-in-the-middle between the client and the Token
Provider. Recall that we assume that the client possesses a bound Provider. Recall that we assume that the client possesses a bound
authentication token (e.g., cookie) for the Token Provider. The man- authentication token (e.g., cookie) for the Token Provider. The man-
in-the-middle can intercept and modify any message sent by the client in-the-middle can intercept and modify any message sent by the client
to the Token Provider, and any message sent by the Token Provider to to the Token Provider, and any message sent by the Token Provider to
the client. (This means, among other things, that the man-in-the- the client. (This means, among other things, that the man-in-the-
middle controls the Javascript running at the client in the origin of middle controls the Javascript running at the client in the origin of
the Token Provider.) It is not, however, in possession of the the Token Provider.) It is not, however, in possession of the
client's Token Binding key. Therefore, it can either choose to client's Token Binding private key. Therefore, it can either choose
replace the Token Binding key in requests from the client to the to replace the Token Binding ID in requests from the client to the
Token Provider, and create a Sec-Token-Binding header field that Token Provider, and create a Sec-Token-Binding header field that
matches the TLS connection between the man-in-the-middle and the matches the TLS connection between the man-in-the-middle and the
Token Provider; or it can choose to leave the Sec-Token-Binding Token Provider; or it can choose to leave the Sec-Token-Binding
header field unchanged. If it chooses the latter, the signature in header field unchanged. If it chooses the latter, the signature in
the Token Binding message (created by the original client on the the Token Binding message (created by the original client on the
exported keying material (EKM) for the connection between client and exported keying material (EKM) for the connection between client and
man-in-the-middle) will not match the EKM between man-in-the-middle man-in-the-middle) will not match a signature on the EKM between man-
and the Token Provider. If it chooses the former (and creates its in-the-middle and the Token Provider. If it chooses the former (and
own signature, with its own Token Binding key, over the EKM for the creates its own signature, using its own Token Binding private key,
connection between man-in-the-middle and Token Provider), then the over the EKM for the connection between itself, the man-in-the-
Token Binding message will match the connection between man-in-the- middle, and Token Provider), then the Token Binding message will
middle and Token Provider, but the Token Binding key in the message match the connection between man-in-the-middle and Token Provider,
will not match the Token Binding key that the client's authentication but the Token Binding ID in the message will not match the Token
token is bound to. Either way, the man-in-the-middle is detected by Binding ID that the client's authentication token is bound to.
the Token Provider, but only if the proof of key possession of the Either way, the man-in-the-middle is detected by the Token Provider,
provided Token Binding key is required in the protocol (as we do but only if the proof of possession of the provided Token Binding
above). private key is required in the protocol (as we do above).
Next, consider the presence of a man-in-the-middle between client and Next, consider the presence of a man-in-the-middle between client and
Token Consumer. That man-in-the-middle can intercept and modify any Token Consumer. That man-in-the-middle can intercept and modify any
message sent by the client to the Token Consumer, and any message message sent by the client to the Token Consumer, and any message
sent by the Token Consumer to the client. The Token Consumer is the sent by the Token Consumer to the client. The Token Consumer is the
party that redirects the client to the Token Provider. In this case, party that redirects the client to the Token Provider. In this case,
the man-in-the-middle controls the redirect URL, and can tamper with the man-in-the-middle controls the redirect URL, and can tamper with
any redirect URL issued by the Token Consumer (as well as with any any redirect URL issued by the Token Consumer (as well as with any
Javascript running in the origin of the Token Consumer). The goal of Javascript running in the origin of the Token Consumer). The goal of
the man-in-the-middle is to trick the Token Issuer to issue a token the man-in-the-middle is to trick the Token Provider to issue a token
bound to _its_ Token Binding key, not to the Token Binding key of the bound to _its_ Token Binding ID, not to the Token Binding ID of the
legitimate client. To thwart this goal of the man-in-the-middle, the legitimate client. To thwart this goal of the man-in-the-middle, the
client's referred Token Binding key must be communicated to the Token client's referred Token Binding ID must be communicated to the Token
Producer in a manner that can not be affected by the man-in-the- Producer in a manner that can not be affected by the man-in-the-
middle (who, as we recall, can modify redirect URLs and Javascript at middle (who, as we recall, can modify redirect URLs and Javascript at
the client). Including the referred Token Binding message in the the client). Including the referred Token Binding structure in the
Sec-Token-Binding header field (as opposed to, say, including the Sec-Token-Binding header field (as opposed to, say, including the
referred Token Binding key in an application-level message as part of referred Token Binding ID in an application-level message as part of
the redirect URL) is one way to assure that the man-in-the-middle the redirect URL) is one way to assure that the man-in-the-middle
between client and Token Consumer cannot affect the communication of between client and Token Consumer cannot affect the communication of
the referred Token Binding key to the Token Provider. the referred Token Binding ID to the Token Provider.
Therefore, the Sec-Token-Binding header field in the federated sign- Therefore, the Sec-Token-Binding header field in the federated sign-
on use case contains both, a proof of possession of the provided on use case contains both: a proof of possession of the provided
Token Binding key, as well as a proof of possession of the referred Token Binding key, as well as a proof of possession of the referred
Token Binding key. Token Binding key.
8. Privacy Considerations 8. Privacy Considerations
8.1. Scoping of Token Binding Keys 8.1. Scoping of Token Binding Key Pairs
Clients use different Token Binding key pairs for different servers, Clients use different Token Binding key pairs for different servers,
so as to not allow Token Binding to become a tracking tool across so as to not allow Token Binding to become a tracking tool across
different servers. However, the scoping of the Token Binding key different servers. However, the scoping of the Token Binding key
pairs to servers varies according to the scoping rules of the pairs to servers varies according to the scoping rules of the
application protocol ([I-D.ietf-tokbind-protocol] section 4.1). application protocol ([I-D.ietf-tokbind-protocol] section 4.1).
In the case of HTTP cookies, servers may use Token Binding to secure In the case of HTTP cookies, servers may use Token Binding to secure
their cookies. These cookies can be attached to any sub-domain of their cookies. These cookies can be attached to any sub-domain of
effective top-level domains, and clients therefore should use the effective top-level domains (eTLDs), and clients therefore should use
same Token Binding key across such subdomains. This will ensure that the same Token Binding key pair across such subdomains. This will
any server capable of receiving the cookie will see the same Token ensure that any server capable of receiving the cookie will see the
Binding ID from the client, and thus be able to verify the token same Token Binding ID from the client, and thus be able to verify the
binding of the cookie. See Section 2.1, above. token binding of the cookie. See Section 2.1, above.
If the client application is not a Web browser, it may have If the client application is not a Web browser, it may have
additional knowledge about the relationship between different additional knowledge about the relationship between different
servers. For example, the client application might be aware of the servers. For example, the client application might be aware of the
fact that two servers play the role of Relying Party and Identity fact that two servers play the role of Relying Party and Identity
Provider in a federated sign-on protocol, and that they therefore Provider in a federated sign-on protocol, and that they therefore
share the identity of the user. In such cases, it is permissible to share the identity of the user. In such cases, it is permissible to
use different Token Binding key scoping rules, such as using the same use different Token Binding key pair scoping rules, such as using the
Token Binding key for both the Relying Party and the Identity same Token Binding key pair for both the Relying Party and the
Provider. Absent such special knowledge, conservative key-scoping Identity Provider. Absent such special knowledge, conservative key-
rules should be used, assuring that clients use different Token scoping rules should be used, assuring that clients use different
Binding keys with different servers. Token Binding key pairs with different servers.
8.2. Life Time of Token Binding Keys 8.2. Life Time of Token Binding Key Pairs
Token Binding keys do not have an expiration time. This means that Token Binding key pairs do not have an expiration time. This means
they can potentially be used by a server to track a user across an that they can potentially be used by a server to track a user across
extended period of time (similar to a long-lived cookie). HTTPS an extended period of time (similar to a long-lived cookie). HTTPS
clients such as web user agents should therefore provide a user clients such as web user agents should therefore provide a user
interface for discarding Token Binding keys (similar to the interface for discarding Token Binding key pairs (similar to the
affordances provided to delete cookies). affordances provided to delete cookies).
If a user agent provides modes such as private browsing mode in which If a user agent provides modes such as private browsing mode in which
the user is promised that browsing state such as cookies are the user is promised that browsing state such as cookies are
discarded after the session is over, the user agent should also discarded after the session is over, the user agent should also
discard Token Binding keys from such modes after the session is over. discard Token Binding key pairs from such modes after the session is
Generally speaking, users should be given the same level of control over. Generally speaking, users should be given the same level of
over life time of Token Binding keys as they have over cookies or control over life time of Token Binding key pairs as they have over
other potential tracking mechanisms. cookies or other potential tracking mechanisms.
8.3. Correlation 8.3. Correlation
An application's various communicating endpoints, that receive Token An application's various communicating endpoints, that receive Token
Binding IDs for TLS connections other than their own, obtain Binding IDs for TLS connections other than their own, obtain
information about the application's other TLS connections (in this information about the application's other TLS connections (in this
context, "an application" is a combination of client-side and server- context, "an application" is a combination of client-side and server-
side components, communicating over HTTPS, where the client side may side components, communicating over HTTPS, where the client side may
be either or both web browser-based or native application-based). be either or both web browser-based or native application-based).
These other Token Binding IDs can serve as correlation handles for These other Token Binding IDs can serve as correlation handles for
skipping to change at page 19, line 17 skipping to change at page 19, line 30
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): this one Specification document(s): this one
Header field name: Include-Referred-Token-Binding-ID Header field name: Include-Referred-Token-Binding-ID
Applicable protocol: HTTP Applicable protocol: HTTP
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): this one Specification document(s): this one
[[TODO: possibly add further considerations wrt the behavior of the
above header fields, per <https://tools.ietf.org/html/
rfc7231#section-8.3>]]
10. Acknowledgements 10. Acknowledgements
This document incorporates comments and suggestions offered by Eric This document incorporates comments and suggestions offered by Eric
Rescorla, Gabriel Montenegro, Martin Thomson, Vinod Anupam, Anthony Rescorla, Gabriel Montenegro, Martin Thomson, Vinod Anupam, Anthony
Nadalin, Michael B. Jones, Bill Cox, Nick Harper, Brian Campbell, Nadalin, Michael B. Jones, Bill Cox, Nick Harper, Brian Campbell,
and others. and others.
11. References 11. References
11.1. Normative References 11.1. Normative References
[fetch-spec] [fetch-spec]
WhatWG, "Fetch", Living Standard , WhatWG, "Fetch", Living Standard ,
<https://fetch.spec.whatwg.org/>. <https://fetch.spec.whatwg.org/>.
[I-D.ietf-tokbind-negotiation] [I-D.ietf-tokbind-negotiation]
Popov, A., Nystrom, M., Balfanz, D., and A. Langley, Popov, A., Nystrom, M., Balfanz, D., and A. Langley,
"Transport Layer Security (TLS) Extension for Token "Transport Layer Security (TLS) Extension for Token
Binding Protocol Negotiation", draft-ietf-tokbind- Binding Protocol Negotiation", draft-ietf-tokbind-
negotiation-05 (work in progress), September 2016. negotiation-06 (work in progress), November 2016.
[I-D.ietf-tokbind-protocol] [I-D.ietf-tokbind-protocol]
Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J. Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J.
Hodges, "The Token Binding Protocol Version 1.0", draft- Hodges, "The Token Binding Protocol Version 1.0", draft-
ietf-tokbind-protocol-10 (work in progress), September ietf-tokbind-protocol-11 (work in progress), November
2016. 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864, Procedures for Message Header Fields", BCP 90, RFC 3864,
DOI 10.17487/RFC3864, September 2004, DOI 10.17487/RFC3864, September 2004,
skipping to change at page 21, line 5 skipping to change at page 21, line 16
[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, [RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication "Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010, Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010,
<http://www.rfc-editor.org/info/rfc5746>. <http://www.rfc-editor.org/info/rfc5746>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012, RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>. <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>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540, Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015, DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>. <http://www.rfc-editor.org/info/rfc7540>.
[RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A., [RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A.,
Langley, A., and M. Ray, "Transport Layer Security (TLS) Langley, A., and M. Ray, "Transport Layer Security (TLS)
Session Hash and Extended Master Secret Extension", Session Hash and Extended Master Secret Extension",
RFC 7627, DOI 10.17487/RFC7627, September 2015, RFC 7627, DOI 10.17487/RFC7627, September 2015,
<http://www.rfc-editor.org/info/rfc7627>. <http://www.rfc-editor.org/info/rfc7627>.
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