GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc8473

Internet Engineering Task Force (IETF) A. Popov Request for Comments: 8473 M. Nystroem Category: Standards Track Microsoft Corp. ISSN: 2070-1721 D. Balfanz, Ed.

                                                             N. Harper
                                                           Google Inc.
                                                             J. Hodges
                                                Kings Mountain Systems
                                                          October 2018
                      Token Binding over HTTP

Abstract

 This document describes a collection of mechanisms that allow HTTP
 servers to cryptographically bind security tokens (such as cookies
 and OAuth tokens) to TLS connections.
 We describe both first-party and federated scenarios.  In a first-
 party scenario, an HTTP server is able to cryptographically bind the
 security tokens that it issues to a client -- and that the client
 subsequently returns to the server -- to the TLS connection between
 the client and the server.  Such bound security tokens are protected
 from misuse, since the server can generally detect if they are
 replayed inappropriately, e.g., over other TLS connections.
 Federated Token Bindings, on the other hand, allow servers to
 cryptographically bind security tokens to a TLS connection that the
 client has with a different server than the one issuing the token.
 This document is a companion document to "The Token Binding Protocol
 Version 1.0" (RFC 8471).

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8473.

Popov, et al. Standards Track [Page 1] RFC 8473 Token Binding over HTTP October 2018

Copyright Notice

 Copyright (c) 2018 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
 2.  The Sec-Token-Binding HTTP Request Header Field . . . . . . .   4
   2.1.  HTTPS Token Binding Key-Pair Scoping  . . . . . . . . . .   5
 3.  TLS Renegotiation . . . . . . . . . . . . . . . . . . . . . .   6
 4.  First-Party Use Cases . . . . . . . . . . . . . . . . . . . .   7
 5.  Federation Use Cases  . . . . . . . . . . . . . . . . . . . .   7
   5.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   7
   5.2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.3.  HTTP Redirects  . . . . . . . . . . . . . . . . . . . . .  10
   5.4.  Negotiated Key Parameters . . . . . . . . . . . . . . . .  12
   5.5.  Federation Example  . . . . . . . . . . . . . . . . . . .  13
 6.  Implementation Considerations . . . . . . . . . . . . . . . .  15
 7.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   7.1.  Security Token Replay . . . . . . . . . . . . . . . . . .  16
   7.2.  Sensitivity of the Sec-Token-Binding Header . . . . . . .  16
   7.3.  Securing Federated Sign-On Protocols  . . . . . . . . . .  17
 8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  20
   8.1.  Scoping of Token Binding Key Pairs  . . . . . . . . . . .  20
   8.2.  Lifetime of Token Binding Key Pairs . . . . . . . . . . .  20
   8.3.  Correlation . . . . . . . . . . . . . . . . . . . . . . .  21
 9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
 10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
   10.1.  Normative References . . . . . . . . . . . . . . . . . .  22
   10.2.  Informative References . . . . . . . . . . . . . . . . .  23
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  25
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

Popov, et al. Standards Track [Page 2] RFC 8473 Token Binding over HTTP October 2018

1. Introduction

 The Token Binding protocol [RFC8471] defines a Token Binding ID for a
 TLS connection between a client and a server.  The Token Binding ID
 of a TLS connection is constructed using the public key of a
 private-public key pair.  The client proves possession of the
 corresponding private key.  This Token Binding key pair is
 long-lived.  That is, subsequent TLS connections between the same
 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 [RFC6749]) to a client, the server can
 include the Token Binding ID in the token, thus cryptographically
 binding the token to TLS connections between that particular client
 and server, and inoculating the token against abuse (reuse, attempted
 impersonation, etc.) by attackers.
 While the Token Binding protocol [RFC8471] defines a message format
 for establishing a Token Binding ID, it does not specify how this
 message is embedded in higher-level protocols.  The purpose of this
 specification is to define how TokenBindingMessages are embedded in
 HTTP (both versions 1.1 [RFC7230] and 2 [RFC7540]).  Note that
 TokenBindingMessages are only defined if the underlying transport
 uses TLS.  This means that Token Binding over HTTP is only defined
 when HTTP is layered on top of TLS (commonly referred to as HTTPS
 [RFC2818]).
 HTTP clients establish a Token Binding ID with a server by including
 a special HTTP header field in HTTP requests.  The HTTP header field
 value is a base64url-encoded TokenBindingMessage.
 A TokenBindingMessage allows a client to establish multiple Token
 Binding IDs with the server by including multiple TokenBinding
 structures.  By default, a client will establish a Provided Token
 Binding ID with the server, indicating a Token Binding ID that the
 client will persistently use with the server.  Under certain
 conditions, the client can also include a Referred Token Binding ID
 in the TokenBindingMessage, indicating a Token Binding ID that the
 client is using with a different server than the one that the
 TokenBindingMessage is sent to.  This is useful in federation
 scenarios.

1.1. Requirements Language

 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.

Popov, et al. Standards Track [Page 3] RFC 8473 Token Binding over HTTP October 2018

2. The Sec-Token-Binding HTTP Request Header Field

 Once a client and server have negotiated the Token Binding protocol
 with HTTP/1.1 or HTTP/2 (see [RFC8471] and [RFC8472]), clients MUST
 include a Sec-Token-Binding header field in their HTTP requests and
 MUST include only one such header field per HTTP request.  Also, the
 Sec-Token-Binding header field MUST NOT be included in HTTP
 responses.  The ABNF of the Sec-Token-Binding header field is (per
 the style of [RFC7230]; see also Section 8.3 of [RFC7231]):
    Sec-Token-Binding = EncodedTokenBindingMessage
 The header field name is Sec-Token-Binding, and its single value,
 EncodedTokenBindingMessage, is a base64url encoding of a single
 TokenBindingMessage, as defined in [RFC8471].  The base64url encoding
 uses the URL and filename safe character set described in Section 5
 of [RFC4648], with all trailing padding characters (i.e., "=")
 omitted and without the inclusion of any line breaks, whitespace, or
 other additional characters.
 For example:
Sec-Token-Binding: AIkAAgBBQFzK4_bhAqLDwRQxqJWte33d7hZ0hZWHwk-miKPg4E\
                   9fcgs7gBPoz-9RfuDfN9WCw6keHEw1ZPQMGs9CxpuHm-YAQM_j\
                   aOwwej6a-cQBGU7CJpUHOvXG4VvjNq8jDsvta9Y8_bPEPj25Gg\
                   mKiPjhJEtZA6mJ_9SNifLvVBTi7fR9wSAAAA
 (Note that the backslashes and line breaks are provided to ease
 readability; they are not part of the actual encoded message.)
 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:
 o  SHOULD NOT be stored by origin servers on PUT requests,
 o  MAY be listed by a server in a Vary response header field, and
 o  MUST NOT be used in HTTP trailers.
 The TokenBindingMessage MUST contain exactly one TokenBinding
 structure with a TokenBindingType value of provided_token_binding,
 which MUST be signed with the Token Binding private key used by the
 client for connections between itself and the server that the HTTP
 request is sent to (clients use different Token Binding key pairs for
 different servers; see Section 2.1 below).  The Token Binding ID

Popov, et al. Standards Track [Page 4] RFC 8473 Token Binding over HTTP October 2018

 established by this TokenBinding is called a "Provided Token
 Binding ID".
 The TokenBindingMessage MAY also contain exactly one TokenBinding
 structure with a TokenBindingType value of referred_token_binding, as
 specified in Section 5.3.  In addition to the latter, or rather than
 the latter, the TokenBindingMessage MAY contain other TokenBinding
 structures.  This is specific to the use case in question; such use
 cases are outside the scope of this specification.
 A TokenBindingMessage is validated by the server as described in
 Section 4.2 ("Server Processing Rules") of [RFC8471].  If validation
 fails and a Token Binding is rejected, any associated bound tokens
 MUST also be rejected by the server.  HTTP requests containing
 invalid tokens MUST be rejected.  In this case, the server
 application MAY return HTTP status code 400 (Bad Request) or proceed
 with an application-specific "invalid token" response (e.g.,
 directing the client to re-authenticate and present a different
 token), or terminate the connection.
 In HTTP/2, the client SHOULD use header compression [RFC7541] to
 avoid the overhead of repeating the same header field in subsequent
 HTTP requests.

2.1. HTTPS Token Binding Key-Pair Scoping

 HTTPS is used in conjunction with various application protocols and
 application contexts, in various ways.  For example, general-purpose
 web browsing is one such HTTP-based application context.  Within that
 context, HTTP cookies [RFC6265] are typically utilized for state
 management, including client authentication.  A related, though
 distinct, example of other HTTP-based application contexts is where
 OAuth tokens [RFC6749] are utilized to manage authorization for
 third-party application access to resources.  The token-scoping rules
 of these two examples can differ: the scoping rules for cookies are
 concisely specified in [RFC6265], whereas OAuth is a framework and
 defines various token types with various scopings, some of which are
 determined by the encompassing application.
 The scoping of Token Binding key pairs generated by web browsers for
 the purpose of binding HTTP cookies MUST be no wider than the
 granularity of a "registered domain" (also known as "effective
 top-level domain + 1", or "eTLD+1").  An origin's "registered domain"
 is the origin's host's public suffix plus the label to its left
 (where the term "public suffix" is defined in the "NOTE:" paragraph
 in Section 5.3 of [RFC6265] as "a domain that is controlled by a
 public registry").  For example, for "https://www.example.com", the
 public suffix (eTLD) is "com", and the registered domain (eTLD+1) is

Popov, et al. Standards Track [Page 5] RFC 8473 Token Binding over HTTP October 2018

 "example.com".  User Agents SHOULD use an up-to-date public suffix
 list, such as the one maintained by Mozilla [PSL].
 This means that in practice the scope of a Token Binding key pair is
 no larger than the scope of a cookie allowed by a web browser.  If a
 web browser restricts cookies to a narrower scope than registered
 domains, the scope of Token Binding key pairs MAY also be narrower.
 This applies to the use of Token Binding key pairs in first-party use
 cases, as well as in federation use cases defined in this
 specification (Section 5).
 Key pairs used to bind other application tokens, such as OAuth tokens
 or "OpenID Connect" ID Tokens [OpenID.Core], SHOULD adhere to the
 above eTLD+1 scoping requirement for those tokens being employed in
 first-party or federation scenarios.  Applications other than web
 browsers MAY use different key-pair scoping rules.  See also
 Section 8.1 below.
 Scoping rules for other HTTP-based application contexts are outside
 the scope of this specification.

3. TLS Renegotiation

 Token Binding over HTTP/1.1 [RFC7230] can be performed in combination
 with TLS renegotiation.  In this case, renegotiation MUST only occur
 between a client's HTTP request and the server's response, the client
 MUST NOT send any pipelined requests, and the client MUST NOT
 initiate renegotiation.  (That is, the client may only send a
 renegotiation ClientHello in response to the server's HelloRequest.)
 These conditions ensure that both the client and the server can
 clearly identify which TLS Exported Keying Material value [RFC5705]
 to use when generating or verifying the TokenBindingMessage.  This
 also prevents a TokenBindingMessage from being split across TLS
 renegotiation boundaries due to TLS message fragmentation; see
 Section 6.2.1 of [RFC5246].
 (Note: This document deals with TLS 1.2 and therefore refers to
 RFC 5246 (which has been obsoleted by RFC 8446); [TOKENBIND-TLS13]
 addresses Token Binding in TLS 1.3.)

Popov, et al. Standards Track [Page 6] RFC 8473 Token Binding over HTTP October 2018

4. First-Party Use Cases

 In a first-party use case (also known as a "same-site" use case), an
 HTTP server issues a security token such as a cookie (or similar) to
 a client and expects the client to return the security token at a
 later time, e.g., in order to authenticate.  Binding the security
 token to the TLS connection between the client and the server
 protects the security token from misuse, since the server can detect
 if the security token is replayed inappropriately, e.g., over other
 TLS connections.
 See Section 5 of [RFC8471] for general guidance regarding the binding
 of security tokens and their subsequent validation.

5. Federation Use Cases

5.1. Introduction

 For privacy reasons, clients use different Token Binding key pairs to
 establish Provided Token Binding IDs with different servers.  As a
 result, a server cannot bind a security token (such as an OAuth token
 or an OpenID Connect ID Token [OpenID.Core]) to a TLS connection that
 the client has with a different server.  This is, however, a common
 requirement in federation scenarios: for example, an Identity
 Provider may wish to issue an identity token to a client and
 cryptographically bind that token to the TLS connection between the
 client and a Relying Party.
 In this section, we describe mechanisms to achieve this.  The common
 idea among these mechanisms is that a server (called the "Token
 Consumer" in this document) signals to the client that it should
 reveal the Provided Token Binding ID that is used between the client
 and itself to another server (called the "Token Provider" in this
 document).  Also common across the mechanisms is how the Token
 Binding ID is revealed to the Token Provider: the client uses the
 Token Binding protocol [RFC8471] and includes a TokenBinding
 structure in the Sec-Token-Binding HTTP header field defined above.
 What differs between the various mechanisms is how the Token Consumer
 signals to the client that it should reveal the Token Binding ID to
 the Token Provider.  Below, we specify one such mechanism, which is
 suitable for redirect-based interactions between Token Consumers and
 Token Providers.

Popov, et al. Standards Track [Page 7] RFC 8473 Token Binding over HTTP October 2018

 Client                        Token Consumer         Token Provider
 +--------+                        +----+                +-----+
 | Client |                        | TC |                | TP  |
 +--------+                        +----+                +-----+
     |                               |                      |
     |                               |                      |
     |                               |                      |
     | Client interacts w/TC         |                      |
     | using TokenBindingID TBID1:   |                      |
     | TBMSG[[provided_token_binding,|                      |
     |        TBID1, signature]]     |                      |
     |------------------------------>|                      |
     |                               |                      |
     | Client interacts w/TP                                |
     | using TokenBindingID TBID2:                          |
     | TBMSG[[provided_token_binding,                       |
     |        TBID2, signature]]                            |
     |----------------------------------------------------->|
     |                                                      |
     |                               |                      |
     | TC signals permission to      |                      |
     | reveal TBID1 to TP            |                      |
     |<------------------------------|                      |
     |                               |                      |
     |                                                      |
     | Client interacts w/TP                                |
     | using TokenBindingID TBID1 and TBID2:                |
     | TBMSG[[provided_token_binding,                       |
     |        TBID2, signature],                            |
     |       [referred_token_binding,                       |
     |        TBID1, signature]]                            |
     |----------------------------------------------------->|
     |                                                      |
     |                               |                      |
     |                               |                      |

5.2. Overview

 In a federated sign-on protocol, an Identity Provider issues an
 identity token to a client, which sends the identity token to a
 Relying Party to authenticate itself.  Examples of this include
 OpenID Connect (in which the identity token is called an "ID Token")
 and the Security Assertion Markup Language (SAML)
 [OASIS.saml-core-2.0-os] (in which the identity token is a SAML
 assertion).

Popov, et al. Standards Track [Page 8] RFC 8473 Token Binding over HTTP October 2018

 To better protect the security of the identity token, the Identity
 Provider may wish to bind the identity token to the TLS connection
 between the client and the Relying Party, thus ensuring that only
 said client can use the identity token.  The Relying Party will
 compare the Token Binding ID (or a cryptographic hash of it) in the
 identity token with the Token Binding ID (or a hash thereof) of the
 TLS connection between this Relying Party and the client.
 This is an example of a federation scenario, which more generally can
 be described as follows:
 o  A Token Consumer causes the client to issue a token request to the
    Token Provider.  The goal is for the client to obtain a token and
    then use it with the Token Consumer.
 o  The client delivers the token request to the Token Provider.
 o  The Token Provider issues the token.  The token is issued for the
    specific Token Consumer who requested it (thus preventing
    malicious Token Consumers from using tokens with other Token
    Consumers).  The token is, however, typically a bearer token,
    meaning that any client can use it with the Token Consumer -- not
    just the client to which it was issued.
 o  Therefore, in the previous step, the Token Provider may want to
    include in the token the Token Binding ID (or a cryptographic hash
    of it) that the client uses when communicating with the Token
    Consumer, thus binding the token to the client's Token Binding key
    pair.  The client proves possession of the private key when
    communicating with the Token Consumer through the Token Binding
    protocol [RFC8471] and uses the corresponding public key of this
    key pair as a component of the Token Binding ID.  Comparing the
    Token Binding ID from the token to the Token Binding ID
    established with the client allows the Token Consumer to verify
    that the token was sent to it by the legitimate client.
 o  To allow the Token Provider to include the Token Binding ID in the
    token, the Token Binding ID between the client and the Token
    Consumer must therefore be communicated to the Token Provider
    along with the token request.  Communicating a Token Binding ID
    involves proving possession of a private key and is described in
    the Token Binding protocol [RFC8471].
 The client will perform this last operation only if the Token
 Consumer requests the client to do so.

Popov, et al. Standards Track [Page 9] RFC 8473 Token Binding over HTTP October 2018

 Below, we specify how Token Consumers can signal this request in
 redirect-based federation protocols.  Note that this assumes that the
 federated sign-on flow starts at the Token Consumer or, at the very
 least, includes a redirect from the Token Consumer to the Token
 Provider.  It is outside the scope of this document to specify
 similar mechanisms for flows that do not include such redirects.

5.3. HTTP Redirects

 When a Token Consumer redirects the client to a Token Provider as a
 means to deliver the token request, it SHOULD include an
 Include-Referred-Token-Binding-ID HTTP response header field in its
 HTTP response.  The ABNF of the Include-Referred-Token-Binding-ID
 header is (per the style of [RFC7230]; see also Section 8.3 of
 [RFC7231]):
    Include-Referred-Token-Binding-ID = "true"
 Where the header field name is "Include-Referred-Token-Binding-ID"
 and the field value of "true" is case insensitive.  For example:
    Include-Referred-Token-Binding-ID: true
 Including this response header field signals to the client that it
 should reveal, to the Token Provider, the Token Binding ID used
 between itself and the Token Consumer.  In the absence of this
 response header field, the client will not disclose any information
 about the Token Binding used between the client and the Token
 Consumer to the Token Provider.
 As illustrated in Section 5.5, when a client receives this header
 field, it should take the TokenBindingID [RFC8471] of the provided
 TokenBinding from the referrer and create a referred TokenBinding
 with it to include in the TokenBindingMessage in the redirect
 request.  In other words, the Token Binding message in the redirect
 request to the Token Provider now includes one provided binding and
 one referred binding, the latter constructed from the binding between
 the client and the Token Consumer.
 When a client receives the Include-Referred-Token-Binding-ID header,
 it includes the referred Token Binding even if both the Token
 Provider and the Token Consumer fall under the same eTLD+1 and the
 provided and Referred Token Binding IDs are the same.
 The referred Token Binding is sent only in the initial request
 resulting from the HTTP response that included the
 Include-Referred-Token-Binding-ID header.  Should the response to
 that initial request be a further redirect, the original referred

Popov, et al. Standards Track [Page 10] RFC 8473 Token Binding over HTTP October 2018

 Token Binding is no longer included in subsequent requests.  (A new
 referred Token Binding may be included if the redirecting endpoint
 itself responded with an Include-Referred-Token-Binding-ID response
 header.)
 If the Include-Referred-Token-Binding-ID header field is
 received in response to a request that did not include the
 Sec-Token-Binding header field, the client MUST ignore the
 Include-Referred-Token-Binding-ID header field.
 This header field only has meaning if the HTTP status code is a
 redirection code (300-399) and MUST be ignored by the client for any
 other status codes.  As described in Section 2, if the client
 supports the Token Binding protocol and has negotiated the Token
 Binding protocol with both the Token Consumer and the Token Provider,
 it sends the Sec-Token-Binding header field to the Token Provider
 with each HTTP request.
 The TokenBindingMessage included in the redirect request to the Token
 Provider SHOULD contain a TokenBinding with a TokenBindingType value
 of referred_token_binding.  If included, this TokenBinding MUST be
 signed with the Token Binding private key used by the client for
 connections between itself and the Token Consumer (more specifically,
 the server that issued the Include-Referred-Token-Binding-ID response
 header field).  The Token Binding ID established by this TokenBinding
 is called a "Referred Token Binding ID".
 As described above, the TokenBindingMessage MUST additionally contain
 a Provided Token Binding ID, i.e., a TokenBinding structure with a
 TokenBindingType value of provided_token_binding, which MUST be
 signed with the Token Binding private key used by the client for
 connections between itself and the Token Provider (more specifically,
 the server that the token request is being sent to).
 If, for some deployment-specific reason, the initial Token Provider
 ("TP1") needs to redirect the client to another Token Provider
 ("TP2") rather than directly back to the Token Consumer, it can be
 accommodated using the header fields defined in this specification in
 the following fashion ("the redirect-chain approach"):
    Initially, the client is redirected to TP1 by the Token Consumer
    ("TC"), as described above.  Upon receiving a client's request
    that contains a TokenBindingMessage that in turn contains both
    provided and referred TokenBindings (for TP1 and TC,
    respectively), TP1 responds to the client with a redirect response
    that (1) contains the Include-Referred-Token-Binding-ID header
    field and (2) directs the client to send a request to TP2.  This
    causes the client to follow the same pattern and send a request

Popov, et al. Standards Track [Page 11] RFC 8473 Token Binding over HTTP October 2018

    containing a TokenBindingMessage that contains both provided and
    referred TokenBindings (for TP2 and TP1, respectively) to TP2.
    Note that this pattern can continue to additional Token Providers.
    In this case, TP2 issues a security token, bound to the client's
    TokenBinding with TP1, and sends a redirect response to the client
    pointing to TP1.  TP1 in turn constructs a security token for the
    Token Consumer, bound to the TC's referred TokenBinding that had
    been conveyed earlier, and sends a redirect response pointing to
    the TC, containing the bound security token, to the client.
 The above is intended as only a non-normative example.  Details are
 specific to deployment contexts.  Other approaches are possible but
 are outside the scope of this specification.

5.4. Negotiated Key Parameters

 The TLS extension for Token Binding protocol negotiation [RFC8472]
 allows the server and client to negotiate the parameters (signature
 algorithm, length) of the Token Binding key pair.  It is possible
 that the Token Binding ID used between the client and the Token
 Consumer, and the Token Binding ID used between the client and the
 Token Provider, use different key parameters.  The client MUST use
 the key parameters negotiated with the Token Consumer in the
 referred_token_binding TokenBinding of the TokenBindingMessage, even
 if those key parameters are different from the ones negotiated with
 the server that the header field is sent to.
 Token Providers SHOULD support all the Token Binding key parameters
 specified in [RFC8471].  If a Token Provider does not support the key
 parameters specified in the referred_token_binding TokenBinding in
 the TokenBindingMessage, it MUST NOT issue a bound token.

Popov, et al. Standards Track [Page 12] RFC 8473 Token Binding over HTTP October 2018

5.5. Federation Example

 The diagram below shows a typical HTTP redirect-based web browser
 single sign-on (SSO) profile (Section 4.1 of
 [OASIS.saml-prof-2.0-os]) (no artifact, no callbacks), featuring the
 binding of, for example, a TLS Token Binding ID into an OpenID
 Connect ID Token.
                                Legend:
 +------------+------------------------------------------------------+
 | EKM:       | TLS Exported Keying Material [RFC5705]               |
 |            |                                                      |
 | {EKMn}Ksm: | EKM for server "n", signed by the private key of     |
 |            | TBID "m", where "n" must represent the server        |
 |            | receiving the ETBMSG.  If a conveyed TB's type is    |
 |            | provided_token_binding, then m = n, else if TB's     |
 |            | type is referred_token_binding, then m != n.  For    |
 |            | example, see step 1b in the diagram below.           |
 |            |                                                      |
 | ETBMSG:    | "Sec-Token-Binding" HTTP header field conveying an   |
 |            | EncodedTokenBindingMessage, in turn conveying        |
 |            | TokenBinding (TB)struct(s), e.g., ETBMSG[[TB]] or    |
 |            | ETBMSG[[TB1],[TB2]]                                  |
 |            |                                                      |
 | ID Token:  | the ID Token in OpenID Connect.  It is the semantic  |
 |            | equivalent of a SAML "authentication assertion".     |
 |            | "ID Token w/TBIDn" denotes a "token bound" ID Token  |
 |            | containing TBIDn.                                    |
 |            |                                                      |
 | Ks and Kp: | private (aka secret) key and public key,             |
 |            | respectively, of the client-side Token Binding key   |
 |            | pair                                                 |
 |            |                                                      |
 | OIDC:      | OpenID Connect                                       |
 |            |                                                      |
 | TB:        | TokenBinding struct containing a signed EKM, TBID,   |
 |            | and TB type, e.g.,                                   |
 |            | [{EKM1}Ks1,TBID1,provided_token_binding]             |
 |            |                                                      |
 | TBIDn:     | Token Binding ID for client and server n's token-    |
 |            | bound TLS association.  TBIDn contains Kpn.          |
 +------------+------------------------------------------------------+

Popov, et al. Standards Track [Page 13] RFC 8473 Token Binding over HTTP October 2018

Client, aka Token Consumer, aka Token Provider, aka User Agent OpenID Client, OpenID Provider,

                         OIDC Relying Party,    OIDC Provider,
                         SAML Relying Party     SAML Identity Provider
                         [ server "1" ]         [ server "2" ]

+——–+ +—-+ +—–+

Client TC TP

+——–+ +—-+ +—–+

  |                               |                      |
  |                               |                      |
  |                               |                      |
  | 0. Client interacts w/TC      |                      |
  | over HTTPS, establishes Ks1 and Kp1, TBID1           |
  | ETBMSG[[{EKM1}Ks1,TBID1,provided_token_binding]]     |
  |------------------------------>|                      |
  |                               |                      |
  |                               |                      |
  |                               |                      |
  | 1a. OIDC ID Token request, aka|                      |
  | "Authentication Request", conveyed with              |
  | an HTTP response header field of                     |
  | Include-Referred-Token-Binding-ID:true.              |
  | Any security-relevant cookies |                      |
  | should contain TBID1.         |                      |
+<- - - - - - - - - - - - - - - - |                      |
. | (redirect to TP via 301, 302, |                      |
. |  303, 307, or 308)            |                      |
. |                               |                      |
+------------------------------------------------------->|
  | 1b. opens HTTPS w/TP,                                |
  | establishes Ks2, Kp2, TBID2;                         |
  | sends a GET or POST with                             |
  | ETBMSG[[{EKM2}Ks2,TBID2,provided_token_binding],     |
  |        [{EKM2}Ks1,TBID1,referred_token_binding]]     |
  | as well as the ID Token request                      |
  |                               |                      |
  |                               |                      |
  |                               |                      |
  | 2. user authentication (if applicable;               |
  |    methods vary; particulars are out of scope)       |
  |<====================================================>|
  | (TP generates ID Token for TC containing TBID1; may  |
  |  also set cookie(s) containing TBID2 and/or TBID1;   |
  |  details vary; particulars are out of scope)         |
  |                               |                      |
  |                               |                      |

Popov, et al. Standards Track [Page 14] RFC 8473 Token Binding over HTTP October 2018

  |                               |                      |
  | 3a. ID Token containing Kp1, issued for TC,          |
  |    conveyed via OIDC "Authentication Response"       |
+<- - - - - - - - - - - - - - - - - - - - - - - - - - - -|
. |   (redirect to TC)            |                      |
. |                               |                      |
. |                               |                      |
+-------------------------------->|                      |
  | 3b. HTTPS GET or POST with                           |
  | ETBMSG[[{EKM1}Ks1,TBID1,provided_token_binding]]     |
  | conveying an Authentication Response containing      |
  | an ID Token w/TBID1, issued for TC                   |
  |                               |                      |
  |                               |                      |
  |                               |                      |
  | 4. user is signed on; any security-relevant cookie(s)|
  | that is set SHOULD contain TBID1                     |
  |<------------------------------|                      |
  |                               |                      |
  |                               |                      |

6. Implementation Considerations

 HTTPS-based applications may have multi-party use cases other than,
 or in addition to, the HTTP redirect-based signaling and conveyance
 of referred Token Bindings, as presented above in Section 5.3.
 Thus, Token Binding implementations should provide APIs for such
 applications to generate Token Binding messages containing Token
 Binding IDs of various application-specified Token Binding types, to
 be conveyed by the Sec-Token-Binding header field.
 However, Token Binding implementations MUST only convey Token Binding
 IDs to servers if signaled to do so by an application.  Signaling
 mechanisms other than the Include-Referred-Token-Binding-ID HTTP
 response header field are possible, but these mechanisms are outside
 the scope of this specification.
 NOTE: See Section 8 ("Privacy Considerations") for privacy guidance
       regarding the use of this functionality.

Popov, et al. Standards Track [Page 15] RFC 8473 Token Binding over HTTP October 2018

7. Security Considerations

7.1. Security Token Replay

 The goal of the federated Token Binding mechanisms is to prevent
 attackers from exporting and replaying tokens used in protocols
 between the client and the Token Consumer, thereby impersonating
 legitimate users and gaining access to protected resources.  Although
 bound tokens can still be replayed by any malware present in clients
 (which may be undetectable to a server), in order to export bound
 tokens to other machines and successfully replay them, attackers also
 need to export the corresponding Token Binding private keys.  Token
 Binding private keys are therefore high-value assets and SHOULD be
 strongly protected, ideally by generating them in a hardware security
 module that prevents key export.
 This consideration is a special case of the scenario described in
 Section 7.1 ("Security Token Replay") of [RFC8471].

7.2. Sensitivity of the Sec-Token-Binding Header

 The purpose of the Token Binding protocol is to convince the server
 that the client that initiated the TLS connection controls a certain
 key pair.  For the server to correctly draw this conclusion after
 processing the Sec-Token-Binding header field, certain secrecy and
 integrity requirements must be met.
 For example, the client must keep its Token Binding private key
 secret.  If the private key is not secret, then another actor in the
 system could create a valid Token Binding header field and thereby
 impersonate the client.  This can render the main purpose of the
 protocol -- to bind bearer tokens to certain clients -- moot.
 Consider, for example, an attacker who obtained (perhaps through a
 network intrusion) an authentication cookie that a client uses with a
 certain server.  Consider further that the server bound that cookie
 to the 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 key, they could then establish a TLS connection with the
 server and craft a Sec-Token-Binding header field that matches the
 binding present in the cookie, thus successfully authenticating as
 the client and gaining access to the client's data at the server.
 The Token Binding protocol, in this case, did not successfully bind
 the cookie to the client.
 Likewise, we need integrity protection of the Sec-Token-Binding
 header field.  A client should not be tricked into sending to a
 server a Sec-Token-Binding header field that contains Token Bindings
 signed with any Token Binding keys that the client does not control.

Popov, et al. Standards Track [Page 16] RFC 8473 Token Binding over HTTP October 2018

 Consider an attacker A that somehow has knowledge of the Exported
 Keying Material (EKM) for a TLS connection between a client C and a
 server S.  (While that is somewhat unlikely, it is also not entirely
 out of the question, since the client might not treat the EKM as a
 secret -- after all, a pre-image-resistant hash function has been
 applied to the TLS master secret, making it impossible for someone
 knowing the 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 could craft a Sec-Token-Binding header
 field with A's key pair over C's EKM.  If the attacker could now
 trick C into sending such a header 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).
 If A has a pre-existing relationship with S (e.g., perhaps has an
 account 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 Token Binding IDs to identify clients but also uses bound
 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
 means -- inserting cookies through JavaScript APIs, setting cookies
 through related-domain attacks, etc.)  In other words, in this
 scenario, A can trick C 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 the account and can thus indirectly observe
 C's behavior (for example, if S has a feature that lets account
 holders see their activity history on S).
 Therefore, we need to protect the integrity of the Sec-Token-Binding
 header field.  One eTLD+1 should not be able to set the
 Sec-Token-Binding header field (through a Document Object Model (DOM)
 API [W3C.REC-DOM-Level-3-Core-20040407] or otherwise) that the User
 Agent uses with another eTLD+1.  Employing the "Sec-" header field
 prefix helps to meet this requirement by denoting the header field
 name as a "forbidden header name"; see [fetch-spec].

7.3. Securing Federated Sign-On Protocols

 As explained above, in a federated sign-on scenario, a client will
 prove possession of two different Token Binding private keys to a
 Token Provider: one private key corresponds to the "provided" Token
 Binding ID (which the client normally uses with the Token Provider),
 and the other is the Token Binding private key corresponding to the
 "referred" Token Binding ID (which the client normally uses with the
 Token Consumer).  The Token Provider is expected to issue a token
 that is bound to the Referred Token Binding ID.

Popov, et al. Standards Track [Page 17] RFC 8473 Token Binding over HTTP October 2018

 Both proofs (that of the provided Token Binding private key and that
 of the referred Token Binding private key) are necessary.  To show
 this, consider the following scenario:
 o  The client has an authentication token with the Token Provider
    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-
    middle) authenticated session with the Token Consumer but has not
    yet done so (in other words, we are about to run the federated
    sign-on protocol).
 o  A man-in-the-middle is allowed to intercept the connection between
    the client and the Token Consumer or between the client and the
    Token Provider (or both).
 The goal is to detect the presence of the man-in-the-middle in these
 scenarios.
 First, consider a man-in-the-middle between the client and the Token
 Provider.  Recall that we assume that the client possesses a bound
 authentication token (e.g., cookie) for the Token Provider.  The
 man-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 the client.  (This means, among other things, that the
 man-in-the-middle controls the JavaScript running at the client in
 the origin of the Token Provider.)  It is not, however, in possession
 of the client's Token Binding private key.  Therefore, it can choose
 to either (1) replace the Token Binding ID in requests from the
 client to the Token Provider and create a Sec-Token-Binding header
 field that matches the TLS connection between the man-in-the-middle
 and the Token Provider or (2) leave the Sec-Token-Binding header
 field unchanged.  If it chooses the latter, the signature in the
 Token Binding message (created by the original client on the EKM for
 the connection between the client and the man-in-the-middle) will not
 match a signature on the EKM between the man-in-the-middle and the
 Token Provider.  If it chooses the former (and creates its own
 signature, using its own Token Binding private key, over the EKM for
 the connection between itself, the man-in-the-middle, and the Token
 Provider), then the Token Binding message will match the connection
 between the man-in-the-middle and the Token Provider, but the Token
 Binding ID in the message will not match the Token Binding ID that
 the client's authentication token is bound to.  Either way, the
 man-in-the-middle is detected by the Token Provider, but only if the
 proof of possession of the provided Token Binding private key is
 required in the protocol (as is done above).

Popov, et al. Standards Track [Page 18] RFC 8473 Token Binding over HTTP October 2018

 Next, consider the presence of a man-in-the-middle between the client
 and the Token Consumer.  That man-in-the-middle can intercept and
 modify any 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 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 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 the man-in-the-middle is to trick the Token Provider into
 issuing a token bound to its Token Binding ID and not to the Token
 Binding ID of the legitimate client.  To thwart this goal of the
 man-in-the-middle, the client's Referred Token Binding ID must be
 communicated to the Token Provider in a manner that cannot be
 affected by the man-in-the-middle (who, as mentioned above, can
 modify redirect URLs and JavaScript at the client).  Including the
 referred TokenBinding structure in the Sec-Token-Binding header field
 (as opposed to, say, including the 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 between the client and the Token
 Consumer cannot affect the communication of the Referred Token
 Binding ID to the Token Provider.
 Therefore, the Sec-Token-Binding header field in the federated
 sign-on use case contains both a proof of possession of the provided
 Token Binding key and a proof of possession of the referred Token
 Binding key.
 Note that the presence of Token Binding does not relieve the Token
 Provider and Token Consumer from performing various checks to ensure
 the security of clients during the use of federated sign-on
 protocols.  These include the following:
 o  The Token Provider should not issue tokens to Token Consumers that
    have been shown to act maliciously.  To aid in this, the
    federation protocol should identify the Token Consumer to the
    Token Provider (e.g., through OAuth client IDs or similar
    mechanisms), and the Token Provider should ensure that tokens are
    indeed issued to the Token Consumer identified in the token
    request (e.g., by verifying that the redirect URI is associated
    with the OAuth client ID).

Popov, et al. Standards Track [Page 19] RFC 8473 Token Binding over HTTP October 2018

 o  The Token Consumer should verify that the tokens were issued for
    it and not for some other Token Consumer.  To aid in this, the
    federation protocol should include an audience parameter in the
    token response or apply equivalent mechanisms (the implicit OAuth
    flow requires Token Consumers to identify themselves when they
    exchange OAuth authorization codes for OAuth refresh tokens,
    leaving it up to the Token Provider to verify that the OAuth
    authorization was delivered to the correct Token Consumer).

8. Privacy Considerations

8.1. Scoping of Token Binding Key Pairs

 Clients use different Token Binding key pairs for different servers,
 so as to not allow Token Binding to become a tracking tool across
 different servers.  However, the scoping of the Token Binding key
 pairs to servers varies according to the scoping rules of the
 application protocol (Section 4.1 of [RFC8471]).
 In the case of HTTP cookies, servers may use Token Binding to secure
 their cookies.  These cookies can be attached to any subdomain of
 effective top-level domains (eTLDs), and clients therefore should use
 the same Token Binding key pair across such subdomains.  This will
 ensure that any server capable of receiving the cookie will see the
 same Token Binding ID from the client and thus be able to verify the
 Token Binding of the cookie.  See Section 2.1 above.
 If the client application is not a web browser, it may have
 additional knowledge about the relationship between different
 servers.  For example, the client application might be aware of the
 fact that two servers play the roles of Relying Party and Identity
 Provider, respectively, in a federated sign-on protocol and that they
 therefore share the identity of the user.  In such cases, it is
 permissible to use different Token Binding key-pair scoping rules,
 such as using the same Token Binding key pair for both the Relying
 Party and the Identity Provider.  Absent such special knowledge,
 conservative key-pair scoping rules should be used, assuring that
 clients use different Token Binding key pairs with different servers.

8.2. Lifetime of Token Binding Key Pairs

 Token Binding key pairs do not have an expiration time.  This means
 that they can potentially be used by a server to track a user for an
 extended period of time (similar to a long-lived cookie).  HTTPS
 clients such as web User Agents SHOULD therefore provide a user
 interface for discarding Token Binding key pairs (similar to the
 controls provided for deleting cookies).

Popov, et al. Standards Track [Page 20] RFC 8473 Token Binding over HTTP October 2018

 If a User Agent provides modes such as private browsing mode in which
 the user is promised that browsing state such as cookies are
 discarded after the session is over, the User Agent MUST also discard
 Token Binding key pairs from such modes after the session is over.
 Generally speaking, users should be given the same level of control
 over the lifetime of Token Binding key pairs as they have over
 cookies or other potential tracking mechanisms.

8.3. Correlation

 An application's various communicating endpoints that receive Token
 Binding IDs for TLS connections other than their own obtain
 information about the application's other TLS connections.  (In this
 context, "an application" is a combination of client-side and
 server-side components, communicating over HTTPS, where the client
 side may be web-browser-based, native-application-based, or both.)
 These other Token Binding IDs can serve as correlation handles for
 the endpoints of the other connections.  If the receiving endpoints
 are otherwise aware of these other connections, then no additional
 information is being exposed.  For instance, if in a redirect-based
 federation protocol the Identity Provider and Relying Party already
 possess URLs for one another, then also having Token Binding IDs for
 these connections does not provide additional correlation
 information.  If not, by providing the other Token Binding IDs,
 additional information is then exposed that can be used to correlate
 the other endpoints.  In such cases, a privacy analysis of enabled
 correlations and their potential privacy impacts should be performed
 as part of the application design decisions of how, and whether, to
 utilize Token Binding.
 Also, Token Binding implementations must take care to only reveal
 Token Binding IDs to other endpoints if signaled to do so by the
 application associated with a Token Binding ID; see Section 6
 ("Implementation Considerations").
 Finally, care should be taken to ensure that unrelated applications
 do not obtain information about each other's Token Bindings.  For
 instance, a Token Binding implementation shared between multiple
 applications on a given system should prevent unrelated applications
 from obtaining each other's Token Binding information.  This may be
 accomplished by using techniques such as application isolation and
 key segregation, depending upon system capabilities.

Popov, et al. Standards Track [Page 21] RFC 8473 Token Binding over HTTP October 2018

9. IANA Considerations

 Below is the Internet Assigned Numbers Authority (IANA) "Permanent
 Message Header Field Names" registration information per [RFC3864].
    Header Field name:           Sec-Token-Binding
    Protocol:                    HTTP
    Status:                      standard
    Reference:                   This document
    Header Field name:           Include-Referred-Token-Binding-ID
    Protocol:                    HTTP
    Status:                      standard
    Reference:                   This document

10. References

10.1. Normative References

 [PSL]      Mozilla, "Public Suffix List",
            <https://publicsuffix.org/>.
 [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>.
 [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
            DOI 10.17487/RFC2818, May 2000,
            <https://www.rfc-editor.org/info/rfc2818>.
 [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
            Procedures for Message Header Fields", BCP 90, RFC 3864,
            DOI 10.17487/RFC3864, September 2004,
            <https://www.rfc-editor.org/info/rfc3864>.
 [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>.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246,
            DOI 10.17487/RFC5246, August 2008,
            <https://www.rfc-editor.org/info/rfc5246>.
 [RFC5705]  Rescorla, E., "Keying Material Exporters for Transport
            Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705,
            March 2010, <https://www.rfc-editor.org/info/rfc5705>.

Popov, et al. Standards Track [Page 22] RFC 8473 Token Binding over HTTP October 2018

 [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
            DOI 10.17487/RFC6265, April 2011,
            <https://www.rfc-editor.org/info/rfc6265>.
 [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>.
 [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
            Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
            DOI 10.17487/RFC7231, June 2014,
            <https://www.rfc-editor.org/info/rfc7231>.
 [RFC7541]  Peon, R. and H. Ruellan, "HPACK: Header Compression for
            HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
            <https://www.rfc-editor.org/info/rfc7541>.
 [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>.
 [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>.

10.2. Informative References

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

Popov, et al. Standards Track [Page 23] RFC 8473 Token Binding over HTTP October 2018

 [OASIS.saml-prof-2.0-os]
            Hughes, J., Ed., Cantor, S., Ed., Hodges, J., Ed., Hirsch,
            F., Ed., Mishra, P., Ed., Philpott, R., Ed., and E. Maler,
            Ed., "Profiles for the OASIS Security Assertion Markup
            Language (SAML) V2.0", OASIS Standard
            OASIS.saml-profiles-2.0-os, March 2005,
            <http://docs.oasis-open.org/security/
            saml/v2.0/saml-profiles-2.0-os.pdf>.
 [OpenID.Core]
            Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
            C. Mortimore, "OpenID Connect Core 1.0 incorporating
            errata set 1", November 2014,
            <http://openid.net/specs/openid-connect-core-1_0.html>.
 [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>.
 [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
            Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
            DOI 10.17487/RFC7540, May 2015,
            <https://www.rfc-editor.org/info/rfc7540>.
 [TOKENBIND-TLS13]
            Harper, N., "Token Binding for Transport Layer Security
            (TLS) Version 1.3 Connections", Work in Progress,
            draft-ietf-tokbind-tls13-01, May 2018.
 [W3C.REC-DOM-Level-3-Core-20040407]
            Le Hors, A., Ed., Le Hegaret, P., Ed., Wood, L., Ed.,
            Nicol, G., Ed., Robie, J., Ed., Champion, M., Ed., and S.
            Byrne, Ed., "Document Object Model (DOM) Level 3 Core
            Specification", World Wide Web Consortium Recommendation
            REC-DOM-Level-3-Core-20040407, April 2004,
            <https://www.w3.org/TR/2004/
            REC-DOM-Level-3-Core-20040407>.

Popov, et al. Standards Track [Page 24] RFC 8473 Token Binding over HTTP October 2018

Acknowledgements

 This document incorporates comments and suggestions offered by Eric
 Rescorla, Gabriel Montenegro, Martin Thomson, Vinod Anupam, Anthony
 Nadalin, Michael B. Jones, Bill Cox, Brian Campbell, and others.
 This document was produced under the chairmanship of John Bradley and
 Leif Johansson.  The area directors included Eric Rescorla, Kathleen
 Moriarty, and Stephen Farrell.

Authors' Addresses

 Andrei Popov
 Microsoft Corp.
 United States of America
 Email: andreipo@microsoft.com
 Magnus Nystroem
 Microsoft Corp.
 United States of America
 Email: mnystrom@microsoft.com
 Dirk Balfanz (editor)
 Google Inc.
 United States of America
 Email: balfanz@google.com
 Nick Harper
 Google Inc.
 United States of America
 Email: nharper@google.com
 Jeff Hodges
 Kings Mountain Systems
 United States of America
 Email: Jeff.Hodges@KingsMountain.com

Popov, et al. Standards Track [Page 25]

/data/webs/external/dokuwiki/data/pages/rfc/rfc8473.txt · Last modified: 2018/10/09 01:36 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki