draft-ietf-httpbis-client-cert-field-00.txt   draft-ietf-httpbis-client-cert-field-01.txt 
HTTP B. Campbell HTTP B. Campbell
Internet-Draft Ping Identity Internet-Draft Ping Identity
Intended status: Informational M. Bishop, Ed. Intended status: Informational M. Bishop, Ed.
Expires: 10 December 2021 Akamai Expires: 29 July 2022 Akamai
8 June 2021 25 January 2022
Client-Cert HTTP Header Field: Conveying Client Certificate Information Client-Cert HTTP Header Field
from TLS Terminating Reverse Proxies to Origin Server Applications draft-ietf-httpbis-client-cert-field-01
draft-ietf-httpbis-client-cert-field-00
Abstract Abstract
This document defines the HTTP header field "Client-Cert" that allows This document defines HTTP extension header fields that allow a TLS
a TLS terminating reverse proxy to convey the client certificate of a terminating reverse proxy to convey the client certificate
mutually-authenticated TLS connection to the origin server in a information of a mutually-authenticated TLS connection to the origin
common and predictable manner. server in a common and predictable manner.
Note to Readers About This Document
_RFC EDITOR: please remove this section before publication_ This note is to be removed before publishing as an RFC.
Discussion of this draft takes place on the HTTP working group Status information for this document may be found at
mailing list (ietf-http-wg@w3.org), which is archived at https://datatracker.ietf.org/doc/draft-ietf-httpbis-client-cert-
https://lists.w3.org/Archives/Public/ietf-http-wg/ field/.
(https://lists.w3.org/Archives/Public/ietf-http-wg/).
Working Group information can be found at http://httpwg.github.io/ Discussion of this document takes place on the HTTP Working Group
(http://httpwg.github.io/); source code and issues list for this mailing list (mailto:ietf-http-wg@w3.org), which is archived at
draft can be found at https://github.com/httpwg/http- https://lists.w3.org/Archives/Public/ietf-http-wg/. Working Group
extensions/labels/client-cert-header (https://github.com/httpwg/http- information can be found at https://httpwg.org/.
extensions/labels/client-cert-header).
Source for this draft and an issue tracker can be found at
https://github.com/httpwg/http-extensions/labels/client-cert-field.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 10 December 2021. This Internet-Draft will expire on 29 July 2022.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2022 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation and Conventions . . . . . . . . . . 4 1.1. Requirements Notation and Conventions . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. HTTP Header Field and Processing Rules . . . . . . . . . . . 4 2. HTTP Header Fields and Processing Rules . . . . . . . . . . . 4
2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Client-Cert HTTP Header Field . . . . . . . . . . . . . . 5 2.2. Client-Cert HTTP Header Field . . . . . . . . . . . . . . 5
2.3. Processing Rules . . . . . . . . . . . . . . . . . . . . 5 2.3. Client-Cert-Chain HTTP Header Field . . . . . . . . . . . 6
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6 2.4. Processing Rules . . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 3. Deployment Considerations . . . . . . . . . . . . . . . . . . 7
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Header Field Compression . . . . . . . . . . . . . . . . 8
5.1. Normative References . . . . . . . . . . . . . . . . . . 7 3.2. Header Block Size . . . . . . . . . . . . . . . . . . . . 8
5.2. Informative References . . . . . . . . . . . . . . . . . 7 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
Appendix B. Considerations Considered . . . . . . . . . . . . . 10 5.1. HTTP Field Name Registrations . . . . . . . . . . . . . . 9
B.1. Header Injection . . . . . . . . . . . . . . . . . . . . 10 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
B.2. The Forwarded HTTP Extension . . . . . . . . . . . . . . 10 6.1. Normative References . . . . . . . . . . . . . . . . . . 10
B.3. The Whole Certificate and Only the Whole Certificate . . 11 6.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 12 Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 12
Appendix D. Document History . . . . . . . . . . . . . . . . . . 13 Appendix B. Considerations Considered . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 B.1. Field Injection . . . . . . . . . . . . . . . . . . . . . 14
B.2. The Forwarded HTTP Extension . . . . . . . . . . . . . . 14
B.3. The Whole Certificate and Certificate Chain . . . . . . . 14
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 15
Appendix D. Document History . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
A fairly common deployment pattern for HTTPS applications is to have A fairly common deployment pattern for HTTPS applications is to have
the origin HTTP application servers sit behind a reverse proxy that the origin HTTP application servers sit behind a reverse proxy that
terminates TLS connections from clients. The proxy is accessible to terminates TLS connections from clients. The proxy is accessible to
the internet and dispatches client requests to the appropriate origin the internet and dispatches client requests to the appropriate origin
server within a private or protected network. The origin servers are server within a private or protected network. The origin servers are
not directly accessible by clients and are only reachable through the not directly accessible by clients and are only reachable through the
reverse proxy. The backend details of this type of deployment are reverse proxy. The backend details of this type of deployment are
skipping to change at page 3, line 25 skipping to change at page 3, line 35
authentication is sometimes employed and in such cases the origin authentication is sometimes employed and in such cases the origin
server often requires information about the client certificate for server often requires information about the client certificate for
its application logic. Such logic might include access control its application logic. Such logic might include access control
decisions, audit logging, and binding issued tokens or cookies to a decisions, audit logging, and binding issued tokens or cookies to a
certificate, and the respective validation of such bindings. The certificate, and the respective validation of such bindings. The
specific details from the certificate needed also vary with the specific details from the certificate needed also vary with the
application requirements. In order for these types of application application requirements. In order for these types of application
deployments to work in practice, the reverse proxy needs to convey deployments to work in practice, the reverse proxy needs to convey
information about the client certificate to the origin application information about the client certificate to the origin application
server. A common way this information is conveyed in practice today server. A common way this information is conveyed in practice today
is by using non-standard headers to carry the certificate (in some is by using non-standard fields to carry the certificate (in some
encoding) or individual parts thereof in the HTTP request that is encoding) or individual parts thereof in the HTTP request that is
dispatched to the origin server. This solution works but dispatched to the origin server. This solution works but
interoperability between independently developed components can be interoperability between independently developed components can be
cumbersome or even impossible depending on the implementation choices cumbersome or even impossible depending on the implementation choices
respectively made (like what header names are used or are respectively made (like what field names are used or are
configurable, which parts of the certificate are exposed, or how the configurable, which parts of the certificate are exposed, or how the
certificate is encoded). A well-known predictable approach to this certificate is encoded). A well-known predictable approach to this
commonly occurring functionality could improve and simplify commonly occurring functionality could improve and simplify
interoperability between independent implementations. interoperability between independent implementations.
This document aspires to standardize an HTTP header field named This document aspires to standardize two HTTP header fields, Client-
"Client-Cert" that a TLS terminating reverse proxy (TTRP) adds to Cert and Client-Cert-Chain, which a TLS terminating reverse proxy
requests that it sends to the backend origin servers. The header (TTRP) adds to requests sent to the backend origin servers. The
value contains the client certificate from the mutually-authenticated Client-Cert field value contains the end-entity client certificate
TLS connection between the originating client and the TTRP. This from the mutually-authenticated TLS connection between the
enables the backend origin server to utilize the client certificate originating client and the TTRP. Optionally, the Client-Cert-Chain
information in its application logic. While there may be additional field value contains the certificate chain used for validation of the
proxies or hops between the TTRP and the origin server (potentially end-entity certificate. This enables the backend origin server to
even with mutually-authenticated TLS connections between them), the utilize the client certificate information in its application logic.
scope of the "Client-Cert" header is intentionally limited to While there may be additional proxies or hops between the TTRP and
exposing to the origin server the certificate that was presented by the origin server (potentially even with mutually-authenticated TLS
the originating client in its connection to the TTRP. connections between them), the scope of the Client-Cert header field
is intentionally limited to exposing to the origin server the
certificate that was presented by the originating client in its
connection to the TTRP.
1.1. Requirements Notation and Conventions 1.1. Requirements Notation and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.2. Terminology 1.2. Terminology
Phrases like TLS client certificate authentication or mutually- Phrases like TLS client certificate authentication or mutually-
authenticated TLS are used throughout this document to refer to the authenticated TLS are used throughout this document to refer to the
process whereby, in addition to the normal TLS server authentication process whereby, in addition to the normal TLS server authentication
with a certificate, a client presents its X.509 certificate [RFC5280] with a certificate, a client presents its X.509 certificate [RFC5280]
and proves possession of the corresponding private key to a server and proves possession of the corresponding private key to a server
when negotiating a TLS connection or the resumption of such a when negotiating a TLS connection or the resumption of such a
connection. In contemporary versions of TLS [RFC8446] [RFC5246] this connection. In contemporary versions of TLS [RFC8446] [RFC5246] this
requires that the client send the Certificate and CertificateVerify requires that the client send the Certificate and CertificateVerify
messages during the handshake and for the server to verify the messages during the handshake and for the server to verify the
CertificateVerify and Finished messages. CertificateVerify and Finished messages.
TODO: HTTP2 forbids TLS renegotiation and post-handshake HTTP/2 restricts TLS 1.2 renegotiation (Section 9.2.1 of [RFC7540])
authentication but it's possible with HTTP1.1 and maybe needs to and prohibits TLS 1.3 post-handshake authentication [RFC8740].
be discussed explicitly here or somewhere in this document? However, they are sometimes used to implement reactive client
Naively I'd say that the "Client-Cert" header will be sent with certificate authentication in HTTP/1.1 [RFC7230] where the server
the data of the most recent client cert anytime after decides whether to request a client certificate based on the HTTP
renegotiation or post-handshake auth. And only for requests that request. HTTP application data sent on such a connection after
are fully covered by the cert but that in practice making the receipt and verification of the client certificate is also mutually-
determination of where exactly in the application data the cert authenticated and thus suitable for the mechanisms described in this
messages arrived is hard to impossible so it'll be a best effort document.
kind of thing.
2. HTTP Header Field and Processing Rules 2. HTTP Header Fields and Processing Rules
2.1. Encoding This document designates the following headers, defined further in
Section 2.2 and Section 2.3 respectively, to carry the client
certificate information of a mutually-authenticated TLS connection
from a reverse proxy to origin server.
The field-values of the HTTP header defined herein utilize the Client-Cert: Conveys the end-entity certificate used by the client
following encoded form. in the TLS handshake with the reverse proxy from the reverse proxy
to the origin server.
A certificate is represented in text as an "EncodedCertificate", Client-Cert-Chain: Conveys the certificate chain used for validation
which is the base64-encoded (Section 4 of [RFC4648]) DER of the end-entity certificate used by the client in the TLS
[ITU.X690.1994] PKIX certificate. The encoded value MUST NOT include handshake from the reverse proxy to the origin server.
any line breaks, whitespace, or other additional characters. ABNF
[RFC5234] syntax for "EncodedCertificate" is shown in the figure
below.
EncodedCertificate = 1*( DIGIT / ALPHA / "+" / "/" ) 0*2"=" 2.1. Encoding
DIGIT = <Defined in Section B.1 of [RFC5234]> ; A-Z / a-z The headers in this document encode certificates as Structured Field
ALPHA = <Defined in Section B.1 of [RFC5234]> ; 0-9 Byte Sequences (Section 3.3.5 of [RFC8941]) where the value of the
binary data is a DER encoded [ITU.X690.1994] X.509 certificate
[RFC5280]. In effect, this means that the binary DER certificate is
encoded using base64 (without line breaks, spaces, or other
characters outside the base64 alphabet) and delimited with colons on
either side.
Note that certificates are often stored encoded in a textual format,
such as the one described in Section 5.1 of [RFC7468], which is
already nearly compatible with a Structured Field Byte Sequence; if
so, it will be sufficient to replace ---(BEGIN|END) CERTIFICATE---
with : and remove line breaks in order to generate an appropriate
item.
2.2. Client-Cert HTTP Header Field 2.2. Client-Cert HTTP Header Field
In the context of a TLS terminating reverse proxy (TTRP) deployment, In the context of a TLS terminating reverse proxy deployment, the
the TTRP makes the TLS client certificate available to the backend proxy makes the TLS client certificate available to the backend
application with the following header field. application with the Client-Cert HTTP header field. This field
contains the end-entity certificate used by the client in the TLS
handshake.
Client-Cert: The end-entity client certificate as an Client-Cert is an Item Structured Header [RFC8941]. Its value MUST
"EncodedCertificate" value. be a Byte Sequence (Section 3.3.5 of [RFC8941]). Its ABNF is:
The "Client-Cert" header field defined herein is only for use in HTTP Client-Cert = sf-binary
requests and MUST NOT be used in HTTP responses. It is a single HTTP
header field-value as defined in Section 3.2 of [RFC7230], which MUST
NOT have a list of values or occur multiple times in a request.
2.3. Processing Rules The value of the header is encoded as described in Section 2.1.
The Client-Cert header field is only for use in HTTP requests and
MUST NOT be used in HTTP responses. It is a single HTTP header field
value as defined in Section 3.2 of [RFC7230], which MUST NOT have a
list of values or occur multiple times in a request.
2.3. Client-Cert-Chain HTTP Header Field
In the context of a TLS terminating reverse proxy deployment, the
proxy MAY make the certificate chain used for validation of the end-
entity certificate available to the backend application with the
Client-Cert-Chain HTTP header field. This field contains
certificates used by the proxy to validate the certificate used by
the client in the TLS handshake. These certificates might or might
not have been provided by the client during the TLS handshake.
Client-Cert-Chain is a List Structured Header [RFC8941]. Each item
in the list MUST be a Byte Sequence (Section 3.3.5 of [RFC8941])
encoded as described in Section 2.1.
The header's ABNF is:
Client-Cert-Chain = sf-list
The Client-Cert-Chain header field is only for use in HTTP requests
and MUST NOT be used in HTTP responses. It MAY have a list of values
or occur multiple times in a request. For header compression
purposes, it might be advantageous to split lists into multiple
instances.
The first certificate in the list SHOULD directly certify the end-
entity certificate provided in the Client-Cert header; each following
certificate SHOULD directly certify the one immediately preceding it.
Because certificate validation requires that trust anchors be
distributed independently, a certificate that specifies a trust
anchor MAY be omitted from the chain, provided that the server is
known to possess any omitted certificates.
However, for maximum compatibility, servers SHOULD be prepared to
handle potentially extraneous certificates and arbitrary orderings.
2.4. Processing Rules
This section outlines the applicable processing rules for a TLS This section outlines the applicable processing rules for a TLS
terminating reverse proxy (TTRP) that has negotiated a mutually- terminating reverse proxy (TTRP) that has negotiated a mutually-
authenticated TLS connection to convey the client certificate from authenticated TLS connection to convey the client certificate from
that connection to the backend origin servers. Use of the technique that connection to the backend origin servers. Use of the technique
is to be a configuration or deployment option and the processing is to be a configuration or deployment option and the processing
rules described herein are for servers operating with that option rules described herein are for servers operating with that option
enabled. enabled.
A TTRP negotiates the use of a mutually-authenticated TLS connection A TTRP negotiates the use of a mutually-authenticated TLS connection
with the client, such as is described in [RFC8446] or [RFC5246], and with the client, such as is described in [RFC8446] or [RFC5246], and
validates the client certificate per its policy and trusted validates the client certificate per its policy and trusted
certificate authorities. Each HTTP request on the underlying TLS certificate authorities. Each HTTP request on the underlying TLS
connection are dispatched to the origin server with the following connection are dispatched to the origin server with the following
modifications: modifications:
1. The client certificate is be placed in the "Client-Cert" header 1. The client certificate is placed in the Client-Cert header field
field of the dispatched request as defined in Section 2.2. of the dispatched request, as described in Section 2.2.
2. Any occurrence of the "Client-Cert" header in the original 2. If so configured, the validation chain of the client certificate
incoming request MUST be removed or overwritten before forwarding is placed in the Client-Cert-Chain header field of the request,
the request. An incoming request that has a "Client-Cert" header as described in Section 2.3.
MAY be rejected with an HTTP 400 response.
3. Any occurrence of the Client-Cert or Client-Cert-Chain header
fields in the original incoming request MUST be removed or
overwritten before forwarding the request. An incoming request
that has a Client-Cert or Client-Cert-Chain header field MAY be
rejected with an HTTP 400 response.
Requests made over a TLS connection where the use of client Requests made over a TLS connection where the use of client
certificate authentication was not negotiated MUST be sanitized by certificate authentication was not negotiated MUST be sanitized by
removing any and all occurrences "Client-Cert" header field prior to removing any and all occurrences of the Client-Cert and Client-Cert-
dispatching the request to the backend server. Chain header fields prior to dispatching the request to the backend
server.
Backend origin servers may then use the "Client-Cert" header of the Backend origin servers may then use the Client-Cert header field of
request to determine if the connection from the client to the TTRP the request to determine if the connection from the client to the
was mutually-authenticated and, if so, the certificate thereby TTRP was mutually-authenticated and, if so, the certificate thereby
presented by the client. presented by the client.
Forward proxies and other intermediaries MUST NOT add the "Client- Forward proxies and other intermediaries MUST NOT add the Client-Cert
Cert" header to requests, or modify an existing "Client-Cert" header. or Client-Cert-Chain header fields to requests, or modify an existing
Similarly, clients MUST NOT employ the "Client-Cert" header in Client-Cert or Client-Cert-Chain header field. Similarly, clients
MUST NOT employ the Client-Cert or Client-Cert-Chain header field in
requests. requests.
A server that receives a request with a "Client-Cert" header value When the value of the Client-Cert request header field is used to
that it considers to be too large can respond with an HTTP 431 status select a response (e.g., the response content is access-controlled),
code per Section 5 of [RFC6585]. the response MUST either be uncacheable (e.g., by sending Cache-
Control: no-store) or be designated for selective reuse only for
subsequent requests with the same Client-Cert header value by sending
a Vary: Client-Cert response header. If a TTRP encounters a response
with a client-cert field name in the Vary header field, it SHOULD
prevent the user agent from caching the response by transforming the
value of the Vary response header field to *.
3. Security Considerations 3. Deployment Considerations
3.1. Header Field Compression
The header described herein enable a TTRP and backend or origin If the client certificate header field is generated by an
server to function together as though, from the client's perspective, intermediary on a connection that compresses fields (e.g., using
they are a single logical server side deployment of HTTPS over a HPACK [RFC7541] or QPACK [I-D.ietf-quic-qpack]) and more than one
mutually-authenticated TLS connection. Use of the "Client-Cert" client's requests are multiplexed into that connection, it can reduce
header outside that intended use case, however, may undermine the compression efficiency significantly, due to the typical size of the
protections afforded by TLS client certificate authentication. field value and its variation between clients. Recipients that
Therefore steps MUST be taken to prevent unintended use, both in anticipate connections with these characteristics can mitigate the
sending the header and in relying on its value. efficiency loss by increasing the size of the dynamic table. If a
recipient does not do so, senders may find it beneficial to always
send the field value as a literal, rather than entering it into the
dynamic table.
Producing and consuming the "Client-Cert" header SHOULD be a 3.2. Header Block Size
configurable option, respectively, in a TTRP and backend server (or
individual application in that server). The default configuration
for both should be to not use the "Client-Cert" header thus requiring
an "opt-in" to the functionality.
In order to prevent header injection, backend servers MUST only A server in receipt of a larger header block than it is willing to
accept the "Client-Cert" header from a trusted TTRP (or other proxy handle can send an HTTP 431 (Request Header Fields Too Large) status
in a trusted path from the TTRP). A TTRP MUST sanitize the incoming code per Section 5 of [RFC6585]. Due to the typical size of the
request before forwarding it on by removing or overwriting any field values containing certificate data, recipients may need to be
existing instances of the header. Otherwise arbitrary clients can configured to allow for a larger maximum header block size. An
control the header value as seen and used by the backend server. It intermediary generating client certificate header fields on
is important to note that neglecting to prevent header injection does connections that allow for advertising the maximum acceptable header
not "fail safe" in that the nominal functionality will still work as block size (e.g. HTTP/2 [RFC7540] or HTTP/3 [I-D.ietf-quic-http])
expected even when malicious actions are possible. As such, extra should account for the additional size of header block of the
care is recommended in ensuring that proper header sanitation is in requests it sends vs. requests it receives by advertising a value to
place. its clients that is sufficiently smaller so as to allow for the
addition of certificate data.
4. Security Considerations
The header fields described herein enable a TTRP and backend or
origin server to function together as though, from the client's
perspective, they are a single logical server side deployment of
HTTPS over a mutually-authenticated TLS connection. Use of the
header fields outside that intended use case, however, may undermine
the protections afforded by TLS client certificate authentication.
Therefore, steps MUST be taken to prevent unintended use, both in
sending the header field and in relying on its value.
Producing and consuming the Client-Cert and Client-Cert-Chain header
fields SHOULD be configurable options, respectively, in a TTRP and
backend server (or individual application in that server). The
default configuration for both should be to not use the header fields
thus requiring an "opt-in" to the functionality.
In order to prevent field injection, backend servers MUST only accept
the Client-Cert and Client-Cert-Chain header fields from a trusted
TTRP (or other proxy in a trusted path from the TTRP). A TTRP MUST
sanitize the incoming request before forwarding it on by removing or
overwriting any existing instances of the fields. Otherwise,
arbitrary clients can control the field values as seen and used by
the backend server. It is important to note that neglecting to
prevent field injection does not "fail safe" in that the nominal
functionality will still work as expected even when malicious actions
are possible. As such, extra care is recommended in ensuring that
proper field sanitation is in place.
The communication between a TTRP and backend server needs to be The communication between a TTRP and backend server needs to be
secured against eavesdropping and modification by unintended parties. secured against eavesdropping and modification by unintended parties.
The configuration options and request sanitization are necessarily The configuration options and request sanitization are necessarily
functionally of the respective servers. The other requirements can functionally of the respective servers. The other requirements can
be met in a number of ways, which will vary based on specific be met in a number of ways, which will vary based on specific
deployments. The communication between a TTRP and backend or origin deployments. The communication between a TTRP and backend or origin
server, for example, might be authenticated in some way with the server, for example, might be authenticated in some way with the
insertion and consumption of the "Client-Cert" header occurring only insertion and consumption of the Client-Cert and Client-Cert-Chain
on that connection. Alternatively the network topology might dictate header fields occurring only on that connection. Alternatively the
a private network such that the backend application is only able to network topology might dictate a private network such that the
accept requests from the TTRP and the proxy can only make requests to backend application is only able to accept requests from the TTRP and
that server. Other deployments that meet the requirements set forth the proxy can only make requests to that server. Other deployments
herein are also possible. that meet the requirements set forth herein are also possible.
4. IANA Considerations 5. IANA Considerations
TODO: register the "Client-Cert" HTTP header field in the registry 5.1. HTTP Field Name Registrations
defined by http-core.
5. References Please register the following entries in the "Hypertext Transfer
Protocol (HTTP) Field Name Registry" defined by
[I-D.ietf-httpbis-semantics]:
5.1. Normative References * Field name: Client-Cert
* Status: permanent
* Specification document: Section 2 of [this document]
* Field name: Client-Cert-Chain
* Status: permanent
* Specification document: Section 2 of [this document]
6. References
6.1. Normative References
[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,
<https://www.rfc-editor.org/rfc/rfc2119>. <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>. <https://www.rfc-editor.org/rfc/rfc5280>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/rfc/rfc4648>.
[ITU.X690.1994] [ITU.X690.1994]
International Telecommunications Union, "Information International Telecommunications Union, "Information
Technology - ASN.1 encoding rules: Specification of Basic Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, 1994. X.690, 1994.
5.2. Informative References [RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
6.2. Informative References
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>. <https://www.rfc-editor.org/rfc/rfc8446>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/rfc/rfc5246>. <https://www.rfc-editor.org/rfc/rfc5246>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Specifications: ABNF", STD 68, RFC 5234, Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/rfc/rfc5234>. <https://www.rfc-editor.org/rfc/rfc7540>.
[RFC8740] Benjamin, D., "Using TLS 1.3 with HTTP/2", RFC 8740,
DOI 10.17487/RFC8740, February 2020,
<https://www.rfc-editor.org/rfc/rfc8740>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014, RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/rfc/rfc7230>. <https://www.rfc-editor.org/rfc/rfc7230>.
[RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX,
PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468,
April 2015, <https://www.rfc-editor.org/rfc/rfc7468>.
[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/rfc/rfc7541>.
[I-D.ietf-quic-qpack]
Krasic, C. '., Bishop, M., and A. Frindell, "QPACK: Header
Compression for HTTP/3", Work in Progress, Internet-Draft,
draft-ietf-quic-qpack-21, 2 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
qpack-21>.
[RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status
Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012, Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012,
<https://www.rfc-editor.org/rfc/rfc6585>. <https://www.rfc-editor.org/rfc/rfc6585>.
[I-D.ietf-quic-http]
Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http-34, 2 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
http-34>.
[I-D.ietf-httpbis-semantics]
Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", Work in Progress, Internet-Draft, draft-ietf-
httpbis-semantics-19, 12 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
semantics-19>.
[RFC7239] Petersson, A. and M. Nilsson, "Forwarded HTTP Extension", [RFC7239] Petersson, A. and M. Nilsson, "Forwarded HTTP Extension",
RFC 7239, DOI 10.17487/RFC7239, June 2014, RFC 7239, DOI 10.17487/RFC7239, June 2014,
<https://www.rfc-editor.org/rfc/rfc7239>. <https://www.rfc-editor.org/rfc/rfc7239>.
[RFC8705] Campbell, B., Bradley, J., Sakimura, N., and T. [RFC8705] Campbell, B., Bradley, J., Sakimura, N., and T.
Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
and Certificate-Bound Access Tokens", RFC 8705, and Certificate-Bound Access Tokens", RFC 8705,
DOI 10.17487/RFC8705, February 2020, DOI 10.17487/RFC8705, February 2020,
<https://www.rfc-editor.org/rfc/rfc8705>. <https://www.rfc-editor.org/rfc/rfc8705>.
[RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/rfc/rfc7250>.
Appendix A. Example Appendix A. Example
In a hypothetical example where a TLS client presents the client and In a hypothetical example where a TLS client presents the client and
intermediate certificate from Figure 1 when establishing a mutually- intermediate certificate from Figure 1 when establishing a mutually-
authenticated TLS connection with the TTRP, the proxy would send the authenticated TLS connection with the TTRP, the proxy would send the
"Client-Cert" header shown in {#example-header} to the backend. Note Client-Cert field shown in {#example-header} to the backend. Note
that line breaks and whitespace have been added to the value of the that line breaks and whitespace have been added to the field value in
header field in Figure 2 for display and formatting purposes only. Figure 2 for display and formatting purposes only.
-----BEGIN CERTIFICATE----- -----BEGIN CERTIFICATE-----
MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJMZXQncyBB MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJMZXQncyBB
dXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0yMDAx dXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0yMDAx
MTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZI MTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZI
zj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p zj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p
5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIw 5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIw
ADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMC ADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMC
BsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1w BsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1w
bGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMje bGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMje
skipping to change at page 10, line 5 skipping to change at page 13, line 5
cml0eTBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABFoaHU+Z5bPKmGzlYXtCf+E6 cml0eTBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABFoaHU+Z5bPKmGzlYXtCf+E6
HYj62fORaHDOrt+yyh3H/rTcs7ynFfGn+gyFsrSP3Ez88rajv+U2NfD0o0uZ4Pmj HYj62fORaHDOrt+yyh3H/rTcs7ynFfGn+gyFsrSP3Ez88rajv+U2NfD0o0uZ4Pmj
YzBhMB0GA1UdDgQWBBTEA2Q6eecKu9g9yb5glbkhhVINGDAfBgNVHSMEGDAWgBTE YzBhMB0GA1UdDgQWBBTEA2Q6eecKu9g9yb5glbkhhVINGDAfBgNVHSMEGDAWgBTE
A2Q6eecKu9g9yb5glbkhhVINGDAPBgNVHRMBAf8EBTADAQH/MA4GA1UdDwEB/wQE A2Q6eecKu9g9yb5glbkhhVINGDAPBgNVHRMBAf8EBTADAQH/MA4GA1UdDwEB/wQE
AwIBhjAKBggqhkjOPQQDAgNIADBFAiEAmAeg1ycKHriqHnaD4M/UDBpQRpkmdcRF AwIBhjAKBggqhkjOPQQDAgNIADBFAiEAmAeg1ycKHriqHnaD4M/UDBpQRpkmdcRF
YGMg1Qyrkx4CIB4ivz3wQcQkGhcsUZ1SOImd/lq1Q0FLf09rGfLQPWDc YGMg1Qyrkx4CIB4ivz3wQcQkGhcsUZ1SOImd/lq1Q0FLf09rGfLQPWDc
-----END CERTIFICATE----- -----END CERTIFICATE-----
Figure 1: Certificate Chain (with client certificate first) Figure 1: Certificate Chain (with client certificate first)
Client-Cert: MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJM Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJ
ZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0y MZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0
MDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZI yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZ
zj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p5Be5 Izj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p5Be
F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIwADAfBgNV 5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIwADAfBgN
HSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMCBsAwEwYDVR0l VHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMCBsAwEwYDVR0
BAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1wbGUuY29tMAoGCCqG lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1wbGUuY29tMAoGCCq
SM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMjeSkC3dFCOOB8TAiEAx/kH GSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMjeSkC3dFCOOB8TAiEAx/k
SB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk= HSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:
Figure 2: Header in HTTP Request to Origin Server Figure 2: Header Field in HTTP Request to Origin Server
Appendix B. Considerations Considered If the proxy were configured to also include the certificate chain,
it would also include this header:
B.1. Header Injection Client-Cert-Chain: :MIIB5jCCAYugAwIBAgIBFjAKBggqhkjOPQQDAjBWMQsw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:, :MIICBjCCAaygAw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:
This draft requires that the TTRP sanitize the headers of the Figure 3: Certificate Chain in HTTP Request to Origin Server
incoming request by removing or overwriting any existing instances of
the "Client-Cert" header before dispatching that request to the Appendix B. Considerations Considered
backend application. Otherwise, a client could inject its own B.1. Field Injection
"Client-Cert" header that would appear to the backend to have come
This draft requires that the TTRP sanitize the fields of the incoming
request by removing or overwriting any existing instances of the
Client-Cert and Client-Cert-Chain header fields before dispatching
that request to the backend application. Otherwise, a client could
inject its own values that would appear to the backend to have come
from the TTRP. Although numerous other methods of detecting/ from the TTRP. Although numerous other methods of detecting/
preventing header injection are possible; such as the use of a unique preventing field injection are possible; such as the use of a unique
secret value as part of the header name or value or the application secret value as part of the field name or value or the application of
of a signature, HMAC, or AEAD, there is no common general a signature, HMAC, or AEAD, there is no common general standardized
standardized mechanism. The potential problem of client header mechanism. The potential problem of client field injection is not at
injection is not at all unique to the functionality of this draft and all unique to the functionality of this draft, and it would therefore
it would therefor be inappropriate for this draft to define a one-off be inappropriate for this draft to define a one-off solution. In the
solution. In the absence of a generic standardized solution existing absence of a generic standardized solution existing currently,
currently, stripping/sanitizing the headers is the de facto means of stripping/sanitizing the fields is the de facto means of protecting
protecting against header injection in practice today. Sanitizing against field injection in practice today. Sanitizing the fields is
the headers is sufficient when properly implemented and is normative sufficient when properly implemented and is a normative requirement
requirement of Section 3. of Section 4.
B.2. The Forwarded HTTP Extension B.2. The Forwarded HTTP Extension
The "Forwarded" HTTP header field defined in [RFC7239] allows proxy The Forwarded HTTP header field defined in [RFC7239] allows proxy
components to disclose information lost in the proxying process. The components to disclose information lost in the proxying process. The
TLS client certificate information of concern to this draft could TLS client certificate information of concern to this draft could
have been communicated with an extension parameter to the "Forwarded" have been communicated with an extension parameter to the Forwarded
header field, however, doing so would have had some disadvantages field; however, doing so would have had some disadvantages that this
that this draft endeavored to avoid. The "Forwarded" header syntax draft endeavored to avoid. The Forwarded field syntax allows for
allows for information about a full chain of proxied HTTP requests, information about a full chain of proxied HTTP requests, whereas the
whereas the "Client-Cert" header of this document is concerned only Client-Cert and Client-Cert-Chain header fields of this document are
with conveying information about the certificate presented by the concerned only with conveying information about the certificate
originating client on the TLS connection to the TTRP (which appears presented by the originating client on the TLS connection to the TTRP
as the server from that client's perspective) to backend (which appears as the server from that client's perspective) to
applications. The multi-hop syntax of the "Forwarded" header is backend applications. The multi-hop syntax of the Forwarded field is
expressive but also more complicated, which would make processing it expressive but also more complicated, which would make processing it
more cumbersome, and more importantly, make properly sanitizing its more cumbersome, and more importantly, make properly sanitizing its
content as required by Section 3 to prevent header injection content as required by Section 4 to prevent field injection
considerably more difficult and error prone. Thus, this draft opted considerably more difficult and error-prone. Thus, this draft opted
for the flatter and more straightforward structure of a single for a flatter and more straightforward structure.
"Client-Cert" header.
B.3. The Whole Certificate and Only the Whole Certificate B.3. The Whole Certificate and Certificate Chain
Different applications will have varying requirements about what Different applications will have varying requirements about what
information from the client certificate is needed, such as the information from the client certificate is needed, such as the
subject and/or issuer distinguished name, subject alternative subject and/or issuer distinguished name, subject alternative
name(s), serial number, subject public key info, fingerprint, etc.. name(s), serial number, subject public key info, fingerprint, etc..
Furthermore some applications, such as "OAuth 2.0 Mutual-TLS Client Furthermore, some applications, such as [RFC8705], make use of the
Authentication and Certificate-Bound Access Tokens" [RFC8705], make entire certificate. In order to accommodate the latter and ensure
use of the entire certificate. In order to accommodate the latter wide applicability by not trying to cherry-pick particular
and ensure wide applicability by not trying to cherry-pick particular
certificate information, this draft opted to pass the full encoded certificate information, this draft opted to pass the full encoded
certificate as the value of the "Client-Cert" header. certificate as the value of the Client-Cert field.
The handshake and validation of the client certificate (chain) of the The handshake and validation of the client certificate (chain) of the
mutually-authenticated TLS connection is performed by the TTRP. With mutually-authenticated TLS connection is performed by the TTRP. With
the responsibility of certificate validation falling on the TTRP, the responsibility of certificate validation falling on the TTRP, the
only the end-entity certificate is passed to the backend - the root end-entity certificate is oftentimes sufficient for the needs of the
Certificate Authority is not included nor are any intermediates. origin server. The separate Client-Cert-Chain field can convey the
certificate chain for deployments that require such information.
TODO: It has been suggested that more information about the
certificate chain might be needed/wanted by the backend
application (to independently evaluate the cert chain, for
example, although that seems like it would be terribly
inefficient) and that any intermediates as well as the root should
also be somehow conveyed, which is an area for further discussion
should this draft progress. One potential approach suggested by a
few folks is to allow some configurability in what is sent along
with maybe a prefix token to indicate what's being sent -
something like "Client-Cert: FULL \<cert> \<intermediate>
\<anchor>" or "Client-Cert: EE \<cert>" as the strawman. Or a
perhaps a parameter or other construct of [RFC8941] to indicate
what's being sent. It's also been suggested that the end-entity
certificate by itself might sometimes be too big (esp. e.g., with
some post-quantum signature schemes). Hard to account for it both
being too much data and not enough data at the same time. But
potentially opening up configuration options to send only specific
attribute(s) from the client certificate is a possibility for
that. In the author's humble opinion the end-entity certificate
by itself strikes a good balance for the vast majority of needs
and avoids optionality. But, again, this is an area for further
discussion should this draft progress.
TODO: It has also been suggested that maybe considerations for
[RFC7250] Raw Public Keys is maybe worth considering. This too is
this is an area for further discussion and consideration should
this draft progress.
Appendix C. Acknowledgements Appendix C. Acknowledgements
The author would like to thank the following individuals who've The authors would like to thank the following individuals who've
contributed in various ways ranging from just being generally contributed in various ways ranging from just being generally
supportive of bringing forth the draft to providing specific feedback supportive of bringing forth the draft to providing specific feedback
or content: or content:
* Evan Anderson * Evan Anderson
* Annabelle Backman * Annabelle Backman
* Mike Bishop * Alan Frindell
* Rory Hewitt * Rory Hewitt
* Fredrik Jeansson * Fredrik Jeansson
* Benjamin Kaduk * Benjamin Kaduk
* Torsten Lodderstedt * Torsten Lodderstedt
* Kathleen Moriarty * Kathleen Moriarty
* Mark Nottingham * Mark Nottingham
* Erik Nygren
* Mike Ounsworth * Mike Ounsworth
* Matt Peterson * Matt Peterson
* Eric Rescorla * Eric Rescorla
* Justin Richer * Justin Richer
* Michael Richardson * Michael Richardson
* Joe Salowey * Joe Salowey
* Rich Salz * Rich Salz
* Mohit Sethi * Mohit Sethi
* Rifaat Shekh-Yusef * Rifaat Shekh-Yusef
* Travis Spencer * Travis Spencer
* Nick Sullivan * Nick Sullivan
* Martin Thomson
* Peter Wu * Peter Wu
* Hans Zandbelt * Hans Zandbelt
Appendix D. Document History Appendix D. Document History
To be removed by the RFC Editor before publication as an RFC To be removed by the RFC Editor before publication as an RFC
draft-ietf-httpbis-client-cert-field-01
* Use RFC 8941 Structured Field Values for HTTP
* Introduce a separate header that can convey the certificate chain
* Add considerations on header compression and size
* Describe interaction with caching
* Fill out IANA Considerations with HTTP field name registrations
* Discuss renegotiation
draft-ietf-httpbis-client-cert-field-00 draft-ietf-httpbis-client-cert-field-00
* Initial WG revision * Initial WG revision
* Mike Bishop added as co-editor * Mike Bishop added as co-editor
draft-bdc-something-something-certificate-05 draft-bdc-something-something-certificate-05
* Change intended status of the draft to Informational * Change intended status of the draft to Informational
* Editorial updates and (hopefully) clarifications * Editorial updates and (hopefully) clarifications
draft-bdc-something-something-certificate-04
* Update reference from draft-ietf-oauth-mtls to RFC8705 * Update reference from draft-ietf-oauth-mtls to RFC8705
draft-bdc-something-something-certificate-03 draft-bdc-something-something-certificate-03
* Expanded further discussion notes to capture some of the feedback * Expanded further discussion notes to capture some of the feedback
in and around the presentation of the draft in SECDISPATCH at IETF in and around the presentation of the draft in SECDISPATCH at IETF
107 and add those who've provided such feedback to the 107 and add those who've provided such feedback to the
acknowledgements acknowledgements
draft-bdc-something-something-certificate-02 draft-bdc-something-something-certificate-02
 End of changes. 71 change blocks. 
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