[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-campbell-tokbind-ttrp) 00 01 02 03 04 05 06 07

Internet Engineering Task Force                              B. Campbell
Internet-Draft                                             Ping Identity
Intended status: Standards Track                        October 19, 2018
Expires: April 22, 2019


        HTTPS Token Binding with TLS Terminating Reverse Proxies
                       draft-ietf-tokbind-ttrp-07

Abstract

   This document defines HTTP header fields that enable a TLS
   terminating reverse proxy to convey information to a backend server
   about the validated Token Binding Message received from a client,
   which enables that backend server to bind, or verify the binding of,
   cookies and other security tokens to the client's Token Binding key.
   This facilitates the reverse proxy and backend server functioning
   together as though they are a single logical server side deployment
   of HTTPS Token Binding.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 22, 2019.

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



Campbell                 Expires April 22, 2019                 [Page 1]


Internet-Draft      Token Binding and TLS Termination       October 2018


   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Notation and Conventions . . . . . . . . . .   3
   2.  HTTP Header Fields and Processing Rules . . . . . . . . . . .   3
     2.1.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . .   4
       2.1.1.  Token Binding ID  . . . . . . . . . . . . . . . . . .   4
       2.1.2.  Token Binding Type  . . . . . . . . . . . . . . . . .   4
     2.2.  Token Binding ID HTTP Header Fields . . . . . . . . . . .   4
     2.3.  Processing Rules  . . . . . . . . . . . . . . . . . . . .   5
     2.4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   6
       2.4.1.  Provided Token Binding ID . . . . . . . . . . . . . .   6
       2.4.2.  Provided and Referred Token Binding IDs . . . . . . .   7
       2.4.3.  Provided and Other  Token Binding IDs . . . . . . . .   8
   3.  TLS Versions and Best Practices . . . . . . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  HTTP Message Header Field Names Registration  . . . . . .  10
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  12
   Appendix B.  Document History . . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Token Binding over HTTP [RFC8473] provides a mechanism that enables
   HTTP servers to cryptographically bind cookies and other security
   tokens to a key generated by the client.  When the use of Token
   Binding is negotiated in the TLS [RFC5246] handshake [RFC8472] the
   client sends an encoded Token Binding Message [RFC8471] as a header
   in each HTTP request, which proves possession of one or more private
   keys held by the client.  The public portion of the keys are
   represented in the Token Binding IDs of the Token Binding Message and
   for each one there is a signature over some data, which includes the
   exported keying material [RFC5705] of the TLS connection.  An HTTP
   server issuing cookies or other security tokens can associate them
   with the Token Binding ID, which ensures those tokens cannot be used
   successfully over a different TLS connection or by a different client
   than the one to which they were issued.

   A fairly common deployment architecture for HTTPS applications is to
   have the backend HTTP application servers sit behind a reverse proxy



Campbell                 Expires April 22, 2019                 [Page 2]


Internet-Draft      Token Binding and TLS Termination       October 2018


   that terminates TLS connections from clients.  The proxy is
   accessible to the internet and dispatches client requests to the
   appropriate backend server within a private or protected network.
   The backend servers are not directly accessible by clients and are
   only reachable through the reverse proxy.  The details of such
   deployments are typically opaque to clients who make requests to the
   proxy server and see responses as though they originated from the
   proxy server itself.  Although HTTPS is also usually employed between
   the proxy and the backend server, the TLS connection that the client
   establishes for HTTPS is between itself and the reverse proxy server.

   Token Binding facilitates a binding of security tokens to a key held
   by the client by way of the TLS connection between that client and
   the server.  In a deployment where TLS is terminated by a reverse
   proxy, however, the TLS connection is between the client and the
   proxy while the backend server is likely the system that will issue
   and validate cookies or other security tokens.  Additional steps are
   therefore needed to enable the use of Token Binding in such
   deployment architectures.  In the absence of a standardized approach,
   different implementations will address it differently, which will
   make interoperability between such implementations difficult or
   impossible without complex configurations or custom integrations.

   This document standardizes HTTP header field names that a TLS
   terminating reverse proxy (TTRP) adds to requests that it sends to
   the backend servers.  The headers contain information from the
   validated Token Binding Message sent by the client to the proxy, thus
   enabling the backend server to bind, or verify the binding of,
   cookies and other security tokens to the client's Token Binding key.
   The usage of the headers, both the TTRP adding the headers and the
   backend application server using the headers to bind cookies or other
   tokens, are to be configuration options of the respective systems as
   they will not always be applicable.

1.1.  Requirements Notation and Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  HTTP Header Fields and Processing Rules








Campbell                 Expires April 22, 2019                 [Page 3]


Internet-Draft      Token Binding and TLS Termination       October 2018


2.1.  Encoding

   The field-values of the HTTP headers defined herein utilize the
   following encoded forms.

2.1.1.  Token Binding ID

   A Token Binding ID is represented as an "EncodedTokenBindingID",
   which is thea base64url encoding of the TokenBindingID byte sequence
   (see section 3 of [RFC8471]) using the URL and filename safe alphabet
   described in Section 5 of [RFC4648], with all trailing pad characters
   '=' omitted and without the inclusion of any line breaks, whitespace,
   or other additional characters.  ABNF [RFC5234] syntax for
   "EncodedTokenBindingID" is shown in Figure 1 below.

     EncodedTokenBindingID = *( DIGIT / ALPHA /  "-" / "_" )

     DIGIT = <Defined in Section B.1 of [RFC5234]>
     ALPHA = <Defined in Section B.1 of [RFC5234]>

                  Figure 1: Encoded Token Binding ID ABNF

2.1.2.  Token Binding Type

   A Token Binding type value (a single byte) can be represented as an
   "EncodedTokenBindingType", which is a case-insensitive hex encoding
   (Section 8 of [RFC4648]).  The ABNF definition is shown in Figure 2
   below.

     EncodedTokenBindingType = 1*2HEXDIG

     HEXDIG = <Defined in Section B.1 of [RFC5234]>

                 Figure 2: Encoded Token Binding Type ABNF

2.2.  Token Binding ID HTTP Header Fields

   The Token Binding Protocol [RFC8471] recommends that implementations
   make Token Binding IDs available to the application as opaque byte
   sequences, enabling those applications to use the Token Binding IDs
   when generating and verifying bound tokens.  In the context of a TLS
   terminating reverse proxy (TTRP) deployment, the TTRP makes the Token
   Binding ID(s) available to the backend application with the following
   header fields.

   Sec-Provided-Token-Binding-ID
      The Token Binding ID of the provided Token Binding represented as
      an "EncodedTokenBindingID".



Campbell                 Expires April 22, 2019                 [Page 4]


Internet-Draft      Token Binding and TLS Termination       October 2018


   Sec-Referred-Token-Binding-ID
      The Token Binding ID of the referred Token Binding represented as
      an "EncodedTokenBindingID".

   Sec-Other-Token-Binding-ID
      Additional Token Bindings that are sent by the client and
      validated by the TTRP are represented as a comma-separated list of
      the concatenation of the "EncodedTokenBindingType", a period (".")
      character, and the "EncodedTokenBindingID" of each.

   Both "Sec-Provided-Token-Binding-ID" and "Sec-Referred-Token-Binding-
   ID" are single HTTP header field-valued as defined in Section 3.2 of
   [RFC7230], which MUST NOT have a list of values or occur multiple
   times in a request.

   All header fields defined herein are only for use in HTTP requests
   and MUST NOT to be used in HTTP responses.

2.3.  Processing Rules

   This section defines the applicable processing rules for a TLS
   terminating reverse proxy (TTRP) and backend server(s) to provide
   server side support of Token Binding over HTTP [RFC8473] using the
   HTTP headers described in Section 2.2.  Use of the technique is to be
   a configuration or deployment option and the processing rules
   described herein are for servers operating with that option enabled.

   A TTRP negotiates the use of Token Binding with the client, such as
   is described in [RFC8472] and validates the Token Binding Message as
   defined in The Token Binding Protocol [RFC8471] and Token Binding
   over HTTP [RFC8473] for each HTTP request on the underlying TLS
   connection.  Requests with a valid Token Binding Message (and meeting
   any other authorization or policy requirements of the TTRP) are
   dispatched to the backend server with the following modifications.

   1.  The "Sec-Token-Binding" header in the original incoming request
       MUST be removed from the request that is dispatched to the
       backend server.

   2.  The Token Binding ID of the provided Token Binding of the Token
       Binding Message MUST be placed in the "Sec-Provided-Token-
       Binding-ID" header field of the dispatched request using the
       format defined in Section 2.2.

   3.  If the Token Binding Message contains a referred Token Binding,
       the referred Token Binding ID MUST be placed in the "Sec-
       Referred-Token-Binding-ID" header field of the dispatched request
       using the format defined in Section 2.2.  Otherwise, the "Sec-



Campbell                 Expires April 22, 2019                 [Page 5]


Internet-Draft      Token Binding and TLS Termination       October 2018


       Referred-Token-Binding-ID" header field MUST NOT be present in
       the dispatched request.

   4.  If the Token Binding Message contains any additional validated
       Token Bindings, they are placed in the "Sec-Other-Token-Binding-
       ID" header field using the format defined in Section 2.2.  If the
       Token Binding Message contains no additional valid Token
       Bindings, the "Sec-Referred-Token-Binding-ID" header field MUST
       NOT be present in the dispatched request.

   5.  Any occurrence of the "Sec-Provided-Token-Binding-ID", "Sec-
       Referred-Token-Binding-ID", and "Sec-Other-Token-Binding-ID"
       headers in the original incoming request MUST be removed or
       overwritten before forwarding the request.

   Requests made over a connection where the use of Token Binding was
   not negotiated MUST be sanitized by removing any occurrences of the
   "Sec-Provided-Token-Binding-ID", "Sec-Referred-Token-Binding-ID", and
   "Sec-Other-Token-Binding-ID" header fields prior to dispatching the
   request to the backend server.

   Forward proxies and other intermediaries MUST NOT add the "Sec-
   Provided-Token-Binding-ID" "Sec-Referred-Token-Binding-ID", or "Sec-
   Other-Token-Binding-ID" header to requests.

2.4.  Examples

   Extra line breaks and whitespace have been added to the following
   examples for display and formatting purposes only.

2.4.1.  Provided Token Binding ID

   The following "Sec-Token-Binding" header is from an HTTP request made
   over a TLS connection between the client and the TTRP where the use
   of Token Binding has been negotiated.  The base64url-encoded
   representation of the exported keying material for that connection is
   "AYVUayPTP9RmELNpGjFl6Ykm2CUx7pUMxe35yb11dgU", which can be used to
   validate the Token Binding Message.  The encoded Token Binding
   Message has the provided Token Binding that the client uses with the
   server.

    Sec-Token-Binding: AIkAAgBBQKzyIrmcY_YCtHVoSHBut69vrGfFdy1_YKTZfFJv
     6BjrZsKD9b9FRzSBxDs1twTqnAS71M1RBumuihhI9xqxXKkAQEtxe4jeUJU0WezxlQ
     XWVSBFeHxFMdXRBIH_LKOSAuSMOJ0XEw1Q8DE248qkOiRKzw3KdSNYukYEPmO21bQi
     3YYAAA

                 Figure 3: Header in HTTP Request to TTRP




Campbell                 Expires April 22, 2019                 [Page 6]


Internet-Draft      Token Binding and TLS Termination       October 2018


   After validating the Token Binding Message, the TTRP removes the
   "Sec-Token-Binding" header and adds the following "Sec-Provided-
   Token-Binding-ID" header with the provided Token Binding ID to the
   request that is dispatched to the backend server.

    Sec-Provided-Token-Binding-ID: AgBBQKzyIrmcY_YCtHVoSHBut69vrGfFdy1_
      YKTZfFJv6BjrZsKD9b9FRzSBxDs1twTqnAS71M1RBumuihhI9xqxXKk

            Figure 4: Header in HTTP Request to Backend Server

2.4.2.  Provided and Referred Token Binding IDs

   The following "Sec-Token-Binding" header is from an HTTP request made
   over a TLS connection between the client and the TTRP where the use
   of Token Binding has been negotiated.  The base64url-encoded
   representation of the exported keying material for that connection is
   "wEWWCP1KPxfq-QL4NxYII_P4ti_9YYqrTpGs28BZEqE", which can be used to
   validate the Token Binding Message.  The encoded Token Binding
   Message has the provided Token Binding that the client uses with the
   server as well as the referred Token Binding that it uses with a
   different server.

    Sec-Token-Binding: ARIAAgBBQCfsI1D1sTq5mvT_2H_dihNIvuHJCHGjHPJchPav
     NbGrOo26-2JgT_IsbvZd4daDFbirYBIwJ-TK1rh8FzrC-psAQMyYIqXj7djGPev1dk
     jV9XxLYGCyqOrBVEtBHrMUCeo22ymLg3OiFcl_fmOPxJbjxI6lKcF0lyfy-dSQmPIe
     zQ0AAAECAEFArPIiuZxj9gK0dWhIcG63r2-sZ8V3LX9gpNl8Um_oGOtmwoP1v0VHNI
     HEOzW3BOqcBLvUzVEG6a6KGEj3GrFcqQBAHQm0pzgUTXKLRamuKE1pmmP9I3UBVpoe
     1DBCe9H2l1VPpsImakUa6crAqZ-0CGBmji7bYzQogpKcyxTTFk5zdwAA

                 Figure 5: Header in HTTP Request to TTRP

   After validating the Token Binding Message, the TTRP removes the
   "Sec-Token-Binding" header and adds the following "Sec-Provided-
   Token-Binding-ID" and "Sec-Referred-Token-Binding-ID" headers, with
   the provided and referred Token Binding IDs respectively, to the
   request that is dispatched to the backend server.

    Sec-Provided-Token-Binding-ID: AgBBQCfsI1D1sTq5mvT_2H_dihNIvuHJCHGj
      HPJchPavNbGrOo26-2JgT_IsbvZd4daDFbirYBIwJ-TK1rh8FzrC-ps
    Sec-Referred-Token-Binding-ID: AgBBQKzyIrmcY_YCtHVoSHBut69vrGfFdy1_
      YKTZfFJv6BjrZsKD9b9FRzSBxDs1twTqnAS71M1RBumuihhI9xqxXKk

            Figure 6: Headers in HTTP Request to Backend Server








Campbell                 Expires April 22, 2019                 [Page 7]


Internet-Draft      Token Binding and TLS Termination       October 2018


2.4.3.  Provided and Other Token Binding IDs

   The following "Sec-Token-Binding" header is from an HTTP request made
   over a TLS connection between the client and the TTRP where the use
   of Token Binding has been negotiated.  The base64url-encoded
   representation of the exported keying material for that connection is
   "Zr_1DESCcDoaltcZCK613UrEWHRf2B3w9i3bwcxpacc", which can be used to
   validate the Token Binding Message.  The encoded Token Binding
   Message has the provided Token Binding and two other Token Bindings.

    Sec-Token-Binding: AZsAAgBBQA35hcCjI5GEHLLAZ0i2l2ZvQe-bSPAP7jovkZJM
     4wYHgmmXNd1aRpnQmXK9ghUmrdtS6p_e2uSlMXIVKOIwgysAQJ-TKyVGF37XUXMy79
     ybwJyPpfCG9Iq6fdIxLX_yJn-L__Z3p_WIL3g17K0OH3XZmJS3qZNNEVu_8HmPN-d9
     hGMAAE0CAEFAR68GbdIQyrHqkorJF0sekYJvf8iV03obGxbaWbqAEJetsYxprB6c3M
     x5KDHBGZjsFbeFW5Xec_EaxX0Hw3RmJwBA-Fu22kokRbB7G0D0g6_sdCHTbczSCmnm
     6rqP1x7kRIIj_kJNCCWcwMMFzbsBTXcm5fJrRdBTcsqiiqYD6aJ1SgAACwIAQUCDqt
     6m63By8b1lvhN-n9OsQThoLomzKpMicSZGwR166jplhbkjrFsHzdNqzLFFEhCT9s0p
     XrcbpOHsZnpRSkmhAEBfOwxjK3Y9EOeMrqjo0IUhmurW2EgtSRBjDwc0r-rDT231Zv
     _f1oePB8Pkd1kgAtgKX5EDiemfo1YER3_I2cv3AAA

                 Figure 7: Header in HTTP Request to TTRP

   After validating the Token Binding Message, the TTRP removes the
   "Sec-Token-Binding" header and adds the following "Sec-Provided-
   Token-Binding-ID" and "Sec-Other-Token-Binding-ID" headers to the
   request that is dispatched to the backend server.

    Sec-Provided-Token-Binding-ID: AgBBQA35hcCjI5GEHLLAZ0i2l2ZvQe-bSPAP
      7jovkZJM4wYHgmmXNd1aRpnQmXK9ghUmrdtS6p_e2uSlMXIVKOIwgys
    Sec-Other-Token-Binding-ID: 4d.AgBBQEevBm3SEMqx6pKKyRdLHpGCb3_IldN6
      GxsW2lm6gBCXrbGMaawenNzMeSgxwRmY7BW3hVuV3nPxGsV9B8N0Zic,B.AgBBQIO
      q3qbrcHLxvWW-E36f06xBOGguibMqkyJxJkbBHXrqOmWFuSOsWwfN02rMsUUSEJP2
      zSletxuk4exmelFKSaE

            Figure 8: Headers in HTTP Request to Backend Server

3.  TLS Versions and Best Practices

   TLS 1.2 [RFC5246] is cited in this document because, at the time of
   writing, it is the latest version that is widely deployed.  However,
   this document is applicable with other TLS versions that allow for
   negotiating the use of Token Binding.  Token Binding for Transport
   Layer Security (TLS) Version 1.3 Connections
   [I-D.ietf-tokbind-tls13], for example, describes Token Binding with
   TLS 1.3 [RFC8446].  Implementation security considerations for TLS,
   including version recommendations, can be found in Recommendations
   for Secure Use of Transport Layer Security (TLS) and Datagram
   Transport Layer Security (DTLS) [BCP195].



Campbell                 Expires April 22, 2019                 [Page 8]


Internet-Draft      Token Binding and TLS Termination       October 2018


4.  Security Considerations

   The headers described herein enable a reverse proxy and backend
   server to function together as though they are a single logical
   server side deployment of HTTPS Token Binding.  Use of the headers
   outside that intended use case, however, may undermine the
   protections afforded by Token Binding.  Therefore steps MUST be taken
   to prevent unintended use, both in sending the headers and in relying
   on their value.

   Producing and consuming the headers SHOULD be a configurable option,
   respectively, in a reverse proxy and backend server (or individual
   application in that server).  The default configuration for both
   should be to not use the headers thus requiring an "opt-in" to the
   functionality.

   Backend servers MUST only accept the headers from trusted reverse
   proxies.  And reverse proxies MUST sanitize the incoming request
   before forwarding it on by removing or overwriting any existing
   instances of the headers.  Otherwise arbitrary clients can control
   the header values as seen and used by the backend server.

   The communication between a reverse proxy and backend server needs to
   be secured against eavesdropping and modification by unintended
   parties.

   The configuration options and request sanitization are necessarily
   functionally of the respective servers.  The other requirements can
   be met in a number of ways, which will vary based on specific
   deployments.  The communication between a reverse proxy and backend
   server, for example, might be over a mutually authenticated TLS with
   the insertion and consumption headers occurring only on that
   connection.  Alternatively the network topology might dictate a
   private network such that the backend application is only able to
   accept requests from the reverse proxy and the proxy can only make
   requests to that server.  Other deployments that meet the
   requirements set forth herein are also possible.

   Employing the "Sec-" header field prefix for the headers defined
   herein denotes them as forbidden header names (see [fetch-spec]),
   which means they cannot be set or modified programmatically by script
   running in-browser.

5.  IANA Considerations







Campbell                 Expires April 22, 2019                 [Page 9]


Internet-Draft      Token Binding and TLS Termination       October 2018


5.1.  HTTP Message Header Field Names Registration

   This document specifies the following new HTTP header fields,
   registration of which is requested in the "Permanent Message Header
   Field Names" registry defined in [RFC3864].

   o  Header Field Name: "Sec-Provided-Token-Binding-ID"
   o  Applicable protocol: HTTP
   o  Status: standard
   o  Author/change Controller: IETF
   o  Specification Document(s): [[ this specification ]]

   o  Header Field Name: "Sec-Referred-Token-Binding-ID"
   o  Applicable protocol: HTTP
   o  Status: standard
   o  Author/change Controller: IETF
   o  Specification Document(s): [[ this specification ]]

   o  Header Field Name: "Sec-Other-Token-Binding-ID"
   o  Applicable protocol: HTTP
   o  Status: standard
   o  Author/change Controller: IETF
   o  Specification Document(s): [[ this specification ]]

6.  References

6.1.  Normative References

   [BCP195]   Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/bcp195>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.




Campbell                 Expires April 22, 2019                [Page 10]


Internet-Draft      Token Binding and TLS Termination       October 2018


   [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>.

   [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>.

   [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>.

   [RFC8473]  Popov, A., Nystroem, M., Balfanz, D., Ed., Harper, N., and
              J. Hodges, "Token Binding over HTTP", RFC 8473,
              DOI 10.17487/RFC8473, October 2018,
              <https://www.rfc-editor.org/info/rfc8473>.

6.2.  Informative References

   [fetch-spec]
              WhatWG, "Fetch", Living Standard ,
              <https://fetch.spec.whatwg.org/>.

   [I-D.ietf-tokbind-tls13]
              Harper, N., "Token Binding for Transport Layer Security
              (TLS) Version 1.3 Connections", draft-ietf-tokbind-
              tls13-01 (work in progress), May 2018.

   [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>.



Campbell                 Expires April 22, 2019                [Page 11]


Internet-Draft      Token Binding and TLS Termination       October 2018


   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

Appendix A.  Acknowledgements

   The author would like to thank the following people for their various
   contributions to the specification: Vinod Anupam, Dirk Balfanz, John
   Bradley, William Denniss, Nick Harper, Jeff Hodges, Subodh Iyengar,
   Leif Johansson, Michael B.  Jones, Yoav Nir, James Manger, Andrei
   Popov, Eric Rescorla, Piotr Sikora, Martin Thomson, and Hans Zandbelt

Appendix B.  Document History

   [[ to be removed by the RFC Editor before publication as an RFC ]]

   draft-ietf-tokbind-ttrp-07

   o  Update TLS 1.3 reference to RFC 8446.

   o  Update the references to the core token binding specs, which are
      now RFCs 8471, 8472, and 8473.

   draft-ietf-tokbind-ttrp-06

   o  Move TLS Versions and Best Practices out of Security
      Considerations to its own top-level section.

   draft-ietf-tokbind-ttrp-05

   o  Editorial updates.

   o  Change one character in the last example to help emphasize the
      case-insensitivity of hex.

   o  Add a TLS Versions and Best Practices section with BCP195 and also
      mention of ietf-tokbind-tls13 and ietf-tls-tls13.

   draft-ietf-tokbind-ttrp-04

   o  Add an example with Sec-Other-Token-Binding-ID.

   o  Use the HEXDIG core ABNF rule for EncodedTokenBindingType and
      mention case-insensitive in the text.

   o  Minor editorial fixes.

   o  Add to the Acknowledgements and remove the 'and others' bit.



Campbell                 Expires April 22, 2019                [Page 12]


Internet-Draft      Token Binding and TLS Termination       October 2018


   draft-ietf-tokbind-ttrp-03

   o  Add a header to allow for additional token binding types other
      than provided and referred to be conveyed.

   o  Reword the Abstract somewhat for (hopefully) improved readability.

   o  Minor editorial and formatting updates.

   draft-ietf-tokbind-ttrp-02

   o  Add to the Acknowledgements.

   o  Update references for Token Binding negotiation, protocol, and
      https.

   o  Use the boilerplate from RFC 8174.

   o  Reformat the "HTTP Header Fields and Processing Rules" section to
      make the header names more prominent and move the encoding
      definitions earlier.

   draft-ietf-tokbind-ttrp-01

   o  Prefix the header names with "Sec-" so that they are denoted as
      forbidden header names by Fetch https://fetch.spec.whatwg.org/

   o  Removed potentially confusing sentence from Security
      Considerations per
      https://mailarchive.ietf.org/arch/msg/unbearable/
      O0IpppyyEqMrQjEkyEi8p8CeBGA

   o  Editorial fixes.

   draft-ietf-tokbind-ttrp-00

   o  Initial WG draft from draft-campbell-tokbind-ttrp.

   draft-campbell-tokbind-ttrp-01

   o  Minor editorial fixes.

   o  Add to the Acknowledgements.

   draft-campbell-tokbind-ttrp-00






Campbell                 Expires April 22, 2019                [Page 13]


Internet-Draft      Token Binding and TLS Termination       October 2018


   o  Initial draft based on 'consensus to work on the problem' from the
      Seoul meeting [1][2] and reflecting the consensus approach from
      discussions at the Chicago meeting [3].

      [1] https://www.ietf.org/proceedings/97/minutes/minutes-97-
      tokbind-01.txt (minutes from Seoul)
      [2] https://www.ietf.org/proceedings/97/slides/slides-97-tokbind-
      reverse-proxies-00.pdf (slides from Seoul)
      [3] https://mailarchive.ietf.org/arch/msg/
      unbearable/_ZHI8y2Vs5WMP8VMRr7zroo_sNU (summary of discussion)

Author's Address

   Brian Campbell
   Ping Identity

   Email: brian.d.campbell@gmail.com


































Campbell                 Expires April 22, 2019                [Page 14]


Html markup produced by rfcmarkup 1.128b, available from https://tools.ietf.org/tools/rfcmarkup/