draft-ietf-httpbis-client-cert-field-06.txt   draft-ietf-httpbis-client-cert-field-latest.txt 
HTTP Working Group B. Campbell Internet Engineering Task Force (IETF) B. Campbell
Internet-Draft Ping Identity Request for Comments: 9440 Ping Identity
Intended status: Informational M. Bishop, Ed. Category: Informational M. Bishop, Ed.
Expires: September 18, 2023 Akamai ISSN: 2070-1721 Akamai
March 17, 2023 July 2023
Client-Cert HTTP Header Field Client-Cert HTTP Header Field
draft-ietf-httpbis-client-cert-field-06
Abstract Abstract
This document describes HTTP extension header fields that allow a TLS This document describes HTTP extension header fields that allow a TLS
terminating reverse proxy to convey the client certificate terminating reverse proxy (TTRP) to convey the client certificate
information of a mutually authenticated TLS connection to the origin information of a mutually authenticated TLS connection to the origin
server in a common and predictable manner. server in a common and
predictable manner.
About This Document About This Document
This note is to be removed before publishing as an RFC. This note is to be removed before publishing as an RFC.
Status information for this document may be found at Status information for this document may be found at
<https://datatracker.ietf.org/doc/draft-ietf-httpbis-client-cert- <https://datatracker.ietf.org/doc/draft-ietf-httpbis-client-cert-
field/>. field/>.
Discussion of this document takes place on the HTTP Working Group Discussion of this document takes place on the HTTP Working Group
mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at
<https://lists.w3.org/Archives/Public/ietf-http-wg/>. Working Group <https://lists.w3.org/Archives/Public/ietf-http-wg/>. Working Group
information can be found at <https://httpwg.org/>. information can be found at <https://httpwg.org/>.
Source for this draft and an issue tracker can be found at Source for this draft and an issue tracker can be found at
<https://github.com/httpwg/http-extensions/labels/client-cert-field>. <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 document is not an Internet Standards Track specification; it is
provisions of BCP 78 and BCP 79. published for informational purposes.
Internet-Drafts are working documents of the Internet Engineering This document is a product of the Internet Engineering Task Force
Task Force (IETF). Note that other groups may also distribute (IETF). It has been approved for publication by the Internet
working documents as Internet-Drafts. The list of current Internet- Engineering Steering Group (IESG). Not all documents approved by the
Drafts is at https://datatracker.ietf.org/drafts/current/. IESG are candidates for any level of Internet Standard; see Section 2
of RFC 7841.
Internet-Drafts are draft documents valid for a maximum of six months Information about the current status of this document, any errata,
and may be updated, replaced, or obsoleted by other documents at any and how to provide feedback on it may be obtained at
time. It is inappropriate to use Internet-Drafts as reference https://www.rfc-editor.org/info/rfc9440.
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 18, 2023.
Copyright Notice Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
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
typically opaque to clients who make requests to the proxy server and typically opaque to clients who make requests to the proxy server and
see responses as though they originated from the proxy server itself. see responses as though they originated from the proxy server itself.
Although HTTPS is also usually employed between the proxy and the Although HTTPS is also usually employed between the proxy and the
origin server, the TLS connection that the client establishes for origin server, the TLS connection that the client establishes for
HTTPS is only between itself and the reverse proxy server. HTTPS is only between itself and the reverse proxy server.
The deployment pattern is found in a number of varieties such as The deployment pattern is found in a number of varieties such as
n-tier architectures, content delivery networks, application load n-tier architectures, content delivery networks, application load-
balancing services, and ingress controllers. balancing services, and ingress controllers.
Although not exceedingly prevalent, TLS client certificate Although not exceedingly prevalent, TLS client certificate
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, including the respective validation of such bindings.
specific details from the certificate needed also vary with the The specific details needed from the certificate 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. At the time of writing, a common way this information is server. At the time of writing, a common way this information is
conveyed is by using non-standard fields to carry the certificate (in conveyed is by using non-standard fields to carry the certificate (in
some encoding) or individual parts thereof in the HTTP request that some encoding) or individual parts thereof in the HTTP request that
is dispatched to the origin server. This solution works but is 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 field 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.
The scope of this document is to describe existing practice while The scope of this document is to describe existing practice while
codifying specific details sufficient to facilitate improved and codifying specific details sufficient to facilitate improved and
lower-touch interoperability. As such, this document describes two lower-touch interoperability. As such, this document describes two
HTTP header fields, "Client-Cert" and "Client-Cert-Chain", which a HTTP header fields, "Client-Cert" and "Client-Cert-Chain", which a
TLS terminating reverse proxy (TTRP) adds to requests sent to the TLS terminating reverse proxy (TTRP) adds to requests sent to the
backend origin servers. The "Client-Cert" field value contains the backend origin servers. The Client-Cert field value contains the
end-entity client certificate from the mutually authenticated TLS end-entity client certificate from the mutually authenticated TLS
connection between the originating client and the TTRP. Optionally, connection between the originating client and the TTRP. Optionally,
the "Client-Cert-Chain" field value contains the certificate chain the Client-Cert-Chain field value contains the certificate chain used
used for validation of the end-entity certificate. This enables the for validation of the end-entity certificate. This enables the
backend origin server to utilize the client certificate information backend origin server to utilize the client certificate information
in its application logic. While there may be additional proxies or in its application logic. While there may be additional proxies or
hops between the TTRP and the origin server (potentially even with hops between the TTRP and the origin server (potentially even with
mutually authenticated TLS connections between them), the scope of mutually authenticated TLS connections between them), the scope of
the "Client-Cert" header field is intentionally limited to exposing the Client-Cert header field is intentionally limited to exposing to
to the origin server the certificate that was presented by the the origin server the certificate that was presented by the
originating client in its connection to the TTRP. 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 "OPTIONAL" in this document are to be interpreted as described in
BCP 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 and Applicability 1.2. Terminology and Applicability
This document uses the following terminology from Section 3 of This document uses the following terminology from Section 3 of
[STRUCTURED-FIELDS] to specify syntax and parsing: List and Byte [STRUCTURED-FIELDS] to specify syntax and parsing: List and Byte
Sequence. Sequence.
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 [TLS] [TLS1.2] this connection. In contemporary versions of TLS [TLS] [TLS1.2], mutual
requires that the client send the Certificate and CertificateVerify authentication requires the client to send the Certificate and
messages during the handshake and for the server to verify the CertificateVerify messages during the handshake and the server to
CertificateVerify and Finished messages. verify the CertificateVerify and Finished messages.
HTTP/2 restricts TLS 1.2 renegotiation (Section 9.2.1 of [RFC9113]) HTTP/2 restricts TLS 1.2 renegotiation (Section 9.2.1 of [RFC9113])
and prohibits TLS 1.3 post-handshake authentication (Section 9.2.3 of and prohibits TLS 1.3 post-handshake authentication (Section 9.2.3 of
[RFC9113]). However, they are sometimes used to implement reactive [RFC9113]). However, they are sometimes used to implement reactive
client certificate authentication in HTTP/1.1 [RFC9112] where the client certificate authentication in HTTP/1.1 [RFC9112] where the
server decides whether to request a client certificate based on the server decides whether to request a client certificate based on the
HTTP request. HTTP application data sent on such a connection after HTTP request. HTTP application data sent on such a connection after
receipt and verification of the client certificate is also mutually receipt and verification of the client certificate is also mutually
authenticated and thus suitable for the mechanisms described in this authenticated and thus suitable for the mechanisms described in this
document. With post-handshake authentication there is also the document. With post-handshake authentication, there is also the
possibility, though unlikely in practice, of multiple certificates possibility, though unlikely in practice, of multiple certificates
and certificate chains from the client on a connection, in which case and certificate chains from the client on a connection. In this
only the certificate and chain of the last post-handshake case, only the certificate and chain of the last post-handshake
authentication are to be utilized for the header fields described authentication are to be utilized for the header fields described
herein. herein.
2. HTTP Header Fields and Processing Rules 2. HTTP Header Fields and Processing Rules
This document designates the following headers, defined further in This document designates the following headers, defined further in
Section 2.2 and Section 2.3 respectively, to carry the client Sections 2.2 and 2.3, respectively, to carry the client certificate
certificate information of a mutually authenticated TLS connection. information of a mutually authenticated TLS connection. The headers
The headers convey the information from the reverse proxy to the convey the information from the reverse proxy to the origin server.
origin server.
Client-Cert: The end-entity certificate used by the client in the Client-Cert: The end-entity certificate used by the client in the
TLS handshake with the reverse proxy. TLS handshake with the reverse proxy.
Client-Cert-Chain: The certificate chain used for validation of the Client-Cert-Chain: The certificate chain used for validation of the
end-entity certificate provided by the client in the TLS handshake end-entity certificate provided by the client in the TLS handshake
with the reverse proxy. with the reverse proxy.
2.1. Encoding 2.1. Encoding
The headers in this document encode certificates as Byte Sequences The headers in this document encode certificates as Byte Sequences
(Section 3.3.5 of [STRUCTURED-FIELDS]) where the value of the binary (Section 3.3.5 of [STRUCTURED-FIELDS]) where the value of the binary
data is a DER encoded [ITU.X690.1994] X.509 certificate [RFC5280]. data is a DER-encoded [ITU.X690.1994] X.509 certificate [RFC5280].
In effect, this means that the binary DER certificate is encoded In effect, this means that the binary DER certificate is encoded
using base64 (without line breaks, spaces, or other characters using base64 (without line breaks, spaces, or other characters
outside the base64 alphabet) and delimited with colons on either outside the base64 alphabet) and delimited with colons on either
side. side.
Note that certificates are often stored encoded in a textual format, Note that certificates are often stored in an encoded textual format,
such as the one described in Section 5.1 of [RFC7468], which is such as the one described in Section 5.1 of [RFC7468], which is
already nearly compatible with a Byte Sequence; if so, it will be already nearly compatible with a Byte Sequence. If certificates are
sufficient to replace "---(BEGIN|END) CERTIFICATE---" with ":" and encoded as such, it will be sufficient to replace "---(BEGIN|END)
remove line breaks in order to generate an appropriate item. 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 deployment, the In the context of a TLS terminating reverse proxy deployment, the
proxy makes the TLS client certificate available to the backend proxy makes the TLS client certificate available to the backend
application with the Client-Cert HTTP header field. This field application with the Client-Cert HTTP header field. This field
contains the end-entity certificate used by the client in the TLS contains the end-entity certificate used by the client in the TLS
handshake. handshake.
Client-Cert is a Byte Sequence with the value of the header encoded Client-Cert is a Byte Sequence with the value of the header encoded
as described in Section 2.1. as described in Section 2.1.
The "Client-Cert" header field is only for use in HTTP requests and The Client-Cert header field is only for use in HTTP requests and
MUST NOT be used in HTTP responses. It is a singleton header field MUST NOT be used in HTTP responses. It is a singleton header field
value as defined in Section 5.5 of [HTTP], which MUST NOT have a list value as defined in Section 5.5 of [HTTP], which MUST NOT have a list
of values or occur multiple times in a request. of values or occur multiple times in a request.
Figure 2 in Appendix A has an example of the "Client-Cert" header Figure 2 in Appendix A has an example of the Client-Cert header
field. field.
2.3. Client-Cert-Chain HTTP Header Field 2.3. Client-Cert-Chain HTTP Header Field
In the context of a TLS terminating reverse proxy deployment, the In the context of a TLS terminating reverse proxy deployment, the
proxy MAY make the certificate chain available to the backend proxy MAY make the certificate chain available to the backend
application with the Client-Cert-Chain HTTP header field. application with the Client-Cert-Chain HTTP header field.
Client-Cert-Chain is a List (Section 3.1 of [STRUCTURED-FIELDS]). Client-Cert-Chain is a List (Section 3.1 of [STRUCTURED-FIELDS]).
Each item in the list MUST be a Byte Sequence encoded as described in Each item in the List MUST be a Byte Sequence encoded as described in
Section 2.1. The order is the same as the ordering in TLS (such as Section 2.1. The order is the same as the ordering in TLS (as
described in Section 4.4.2 of [TLS]). described in Section 4.4.2 of [TLS]).
Client-Cert-Chain MUST NOT appear unless Client-Cert is also present, Client-Cert-Chain MUST NOT appear unless Client-Cert is also present,
and it does not itself include the end-entity certificate that is and it does not itself include the end-entity certificate that is
already present in Client-Cert. The root certificate MAY be omitted already present in Client-Cert. The root certificate MAY be omitted
from Client-Cert-Chain, provided that the target origin server is from Client-Cert-Chain, provided that the target origin server is
known to possess the omitted trust anchor. known to possess the omitted trust anchor.
The "Client-Cert-Chain" header field is only for use in HTTP requests 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 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 or occur multiple times in a request. For header compression
purposes, it might be advantageous to split lists into multiple purposes, it might be advantageous to split lists into multiple
instances. instances.
Figure 3 in Appendix A has an example of the "Client-Cert-Chain" Figure 3 in Appendix A has an example of the Client-Cert-Chain header
header field. field.
2.4. Processing Rules 2.4. Processing Rules
This section outlines the applicable processing rules for a TLS This section outlines the applicable processing rules for a TTRP that
terminating reverse proxy (TTRP) that has negotiated a mutually has negotiated a mutually authenticated TLS connection to convey the
authenticated TLS connection to convey the client certificate from client certificate from that connection to the backend origin
that connection to the backend origin servers. Use of the technique servers. This technique is to be used as a configuration or
is to be a configuration or deployment option and the processing deployment option, and the processing rules described herein are for
rules described herein are for servers operating with that option 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 [TLS] or [TLS1.2], and with the client, such as is described in [TLS] or [TLS1.2], 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 is dispatched to the origin server with the following connection is dispatched to the origin server with the following
modifications: modifications:
1. The client certificate is placed in the "Client-Cert" header 1. The client certificate is placed in the Client-Cert header field
field of the dispatched request, as described in Section 2.2. of the dispatched request, as described in Section 2.2.
2. If so configured, the validation chain of the client certificate 2. If so configured, the validation chain of the client certificate
is placed in the "Client-Cert-Chain" header field of the request, is placed in the Client-Cert-Chain header field of the request,
as described in Section 2.3. as described in Section 2.3.
3. Any occurrence of the "Client-Cert" or "Client-Cert-Chain" header 3. Any occurrence of the Client-Cert or Client-Cert-Chain header
fields in the original incoming request MUST be removed or fields in the original incoming request MUST be removed or
overwritten before forwarding the request. An incoming request overwritten before forwarding the request. An incoming request
that has a "Client-Cert" or "Client-Cert-Chain" header field MAY that has a Client-Cert or Client-Cert-Chain header field MAY be
be rejected with an HTTP 400 response. rejected with an HTTP 400 response.
Requests to the TTRP made over a TLS connection where the use of Requests to the TTRP made over a TLS connection where the use of
client certificate authentication was not negotiated MUST be client certificate authentication was not negotiated MUST be
sanitized by removing any and all occurrences of the "Client-Cert" sanitized by removing any and all occurrences of the Client-Cert and
and "Client-Cert-Chain" header fields prior to dispatching the Client-Cert-Chain header fields prior to dispatching the request to
request to the backend server. the backend server.
Backend origin servers may then use the "Client-Cert" header field of Backend origin servers may then use the Client-Cert header field of
the request to determine if the connection from the client to the the request to determine if the connection from the client to the
TTRP was mutually authenticated and, if so, the certificate thereby TTRP was mutually authenticated and, if so, the certificate thereby
presented by the client. Access control decisions based on the presented by the client. Access control decisions based on the
client certificate (or lack thereof) can be conveyed by selecting client certificate (or lack thereof) can be conveyed by selecting
response content as appropriate or with an HTTP 403 response, if the response content as appropriate or with an HTTP 403 response, if the
certificate is deemed unacceptable for the given context. Note that certificate is deemed unacceptable for the given context. Note that
TLS clients that rely on error indications at the TLS layer for an TLS clients that rely on error indications at the TLS layer for an
unacceptable certificate will not receive those signals. unacceptable certificate will not receive those signals.
When the value of the "Client-Cert" request header field is used to When the value of the Client-Cert request header field is used to
select a response (e.g., the response content is access-controlled), select a response (e.g., the response content is access-controlled),
the response MUST either be uncacheable (e.g., by sending "Cache- the response MUST either be uncacheable (e.g., by sending "Cache-
Control: no-store") or be designated for selective reuse only for Control: no-store") or be designated for selective reuse only for
subsequent requests with the same "Client-Cert" header value by subsequent requests with the same Client-Cert header field value by
sending a "Vary: Client-Cert" response header. If a TTRP encounters sending a "Vary: Client-Cert" response header. If a TTRP encounters
a response with a "client-cert" field name in the "Vary" header a response with Client-Cert or Client-Cert-Chain in the Vary header
field, it SHOULD prevent the user agent from caching the response by field (Section 12.5.5 of [HTTP]), it SHOULD prevent the user agent
transforming the value of the "Vary" response header field to "*". from caching the response by transforming the value of the Vary
response header field to "*".
Forward proxies and other intermediaries MUST NOT add the "Client- Forward proxies and other intermediaries MUST NOT add the Client-Cert
Cert" or "Client-Cert-Chain" header fields to requests, or modify an or Client-Cert-Chain header fields to requests or modify an existing
existing "Client-Cert" or "Client-Cert-Chain" header field. Client-Cert or Client-Cert-Chain header field. Similarly, clients
Similarly, clients MUST NOT employ the "Client-Cert" or "Client-Cert- MUST NOT employ the Client-Cert or Client-Cert-Chain header field in
Chain" header field in requests. requests.
3. Deployment Considerations 3. Deployment Considerations
3.1. Header Field Compression 3.1. Header Field Compression
If the connection between the TTRP and origin is capable of field If the connection between the TTRP and origin is capable of field
compression (e.g., HPACK [HPACK] or QPACK [QPACK]), and the TTRP compression (e.g., HPACK [HPACK] or QPACK [QPACK]), and the TTRP
multiplexes more than one client's requests into that connection, the multiplexes more than one client's requests into that connection, the
size and variation of "Client-Cert" and "Client-Cert-Chain" field size and variation of Client-Cert and Client-Cert-Chain field values
values can reduce compression efficiency significantly. An origin can reduce compression efficiency significantly. An origin could
could mitigate the efficiency loss by increasing the size of the mitigate the efficiency loss by increasing the size of the dynamic
dynamic table. If the TTRP determines that the origin dynamic table table. If the TTRP determines that the origin dynamic table is not
is not sufficiently large, it may find it beneficial to always send sufficiently large, it may find it beneficial to always send the
the field value as a literal, rather than entering it into the table. field value as a literal rather than entering it into the table.
3.2. Message Header Size 3.2. Message Header Size
A server in receipt of a larger message header than it is willing to A server in receipt of a larger message header than it is willing to
handle can send an HTTP 431 (Request Header Fields Too Large) status handle can send an HTTP 431 (Request Header Fields Too Large) status
code per Section 5 of [RFC6585]. Due to the typical size of the code per Section 5 of [RFC6585]. Due to the typical size of the
field values containing certificate data, recipients may need to be field values containing certificate data, recipients may need to be
configured to allow for a larger maximum header size. An configured to allow for a larger maximum header size. An
intermediary generating client certificate header fields on intermediary generating client certificate header fields on
connections that allow for advertising the maximum acceptable header connections that allow for advertising the maximum acceptable header
size (e.g., HTTP/2 [RFC9113] or HTTP/3 [RFC9114]) should account for size (e.g., HTTP/2 [RFC9113] or HTTP/3 [RFC9114]) should account for
the additional size of the header of the requests it sends vs. the additional size of the header of the requests it sends, versus
requests it receives by advertising a value to its clients that is the requests it receives, by advertising a value to its clients that
sufficiently smaller so as to allow for the addition of certificate is sufficiently smaller so as to allow for the addition of
data. certificate data.
3.3. TLS Session Resumption 3.3. TLS Session Resumption
Some TLS implementations do not retain client certificate information Some TLS implementations do not retain client certificate information
when resuming. Providing inconsistent values of Client-Cert and when resuming. Providing inconsistent values of Client-Cert and
Client-Cert-Chain when resuming might lead to errors, so Client-Cert-Chain when resuming might lead to errors, so
implementations that are unable to provide these values SHOULD either implementations that are unable to provide these values SHOULD either
disable resumption for connections with client certificates or disable resumption for connections with client certificates or
initially omit a "Client-Cert" or "Client-Cert-Chain" field if it initially omit a Client-Cert or Client-Cert-Chain field if it might
might not be available after resuming. not be available after resuming.
4. Security Considerations 4. Security Considerations
The header fields described herein enable a TTRP and backend or The header fields described herein enable a TTRP and backend or
origin server to function together as though, from the client's origin server to function together as though, from the client's
perspective, they are a single logical server-side deployment of perspective, they are a single logical server-side deployment of
HTTPS over a mutually authenticated TLS connection. Use of the HTTPS over a mutually authenticated TLS connection. However, use of
header fields outside that intended use case, however, may undermine the header fields outside that intended use case may undermine the
the protections afforded by TLS client certificate authentication. protections afforded by TLS client certificate authentication.
Therefore, steps such as those described below need to be taken to Therefore, steps such as those described below need to be taken to
prevent unintended use, both in sending the header field and in prevent unintended use, both in sending the header field and in
relying on its value. relying on its value.
Producing and consuming the "Client-Cert" and "Client-Cert-Chain" Producing and consuming the Client-Cert and Client-Cert-Chain header
header fields SHOULD be configurable options, respectively, in a TTRP fields SHOULD be configurable options, respectively, in a TTRP and
and backend server (or individual application in that server). The backend server (or in an individual application in that server). The
default configuration for both should be to not use the header default configuration for both should be to not use the header
fields, thus requiring an "opt-in" to the functionality. fields, thus requiring an "opt-in" to the functionality.
In order to prevent field injection, backend servers MUST only accept In order to prevent field injection, backend servers MUST only accept
the "Client-Cert" and "Client-Cert-Chain" header fields from a the Client-Cert and Client-Cert-Chain header fields from a trusted
trusted TTRP (or other proxy in a trusted path from the TTRP). A TTRP (or other proxy in a trusted path from the TTRP). A TTRP MUST
TTRP MUST sanitize the incoming request before forwarding it on by sanitize the incoming request before forwarding it on by removing or
removing or overwriting any existing instances of the fields. overwriting any existing instances of the fields. Otherwise,
Otherwise, arbitrary clients can control the field values as seen and arbitrary clients can control the field values as seen and used by
used by the backend server. It is important to note that neglecting the backend server. It is important to note that neglecting to
to prevent field injection does not "fail safe" in that the nominal prevent field injection does not "fail safe" in that the nominal
functionality will still work as expected even when malicious actions functionality will still work as expected even when malicious actions
are possible. As such, extra care is recommended in ensuring that are possible. As such, extra care is recommended in ensuring that
proper field sanitation is in place. 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 necessary The configuration options and request sanitization are necessary
functionality of the respective servers. The other requirements can functionalities of the respective servers. The other requirements
be met in a number of ways, which will vary based on specific can 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" and "Client-Cert- insertion and consumption of the Client-Cert and Client-Cert-Chain
Chain" header fields occurring only on that connection. Appendix B.3 header fields occurring only on that connection. Appendix B.3 of
of [HTTPSIG] gives one example of this with an application of HTTP [HTTPSIG] gives one example of this with an application of HTTP
Message Signatures. Alternatively, the network topology might Message Signatures. Alternatively, the network topology might
dictate a private network such that the backend application is only dictate a private network such that the backend application is only
able to accept requests from the TTRP and the proxy can only make able to accept requests from the TTRP and the proxy can only make
requests to that server. Other deployments that meet the requests to that server. Other deployments that meet the
requirements set forth herein are also possible. requirements set forth herein are also possible.
5. IANA Considerations 5. IANA Considerations
5.1. HTTP Field Name Registrations 5.1. HTTP Field Name Registrations
Please register the following entries in the "Hypertext Transfer IANA has registered the following entries in the "Hypertext Transfer
Protocol (HTTP) Field Name Registry" defined by HTTP Semantics Protocol (HTTP) Field Name Registry" defined by "HTTP Semantics"
[HTTP]: [HTTP]:
o Field name: Client-Cert +-------------------+-----------+----------------------+
| Field Name | Status | Reference |
o Status: permanent +-------------------+-----------+----------------------+
| Client-Cert | permanent | RFC 9440, Section 2 |
o Specification document: Section 2 of [this document] | | | |
| Client-Cert-Chain | permanent | RFC 9440, Section 2 |
o Field name: Client-Cert-Chain +-------------------+-----------+----------------------+
o Status: permanent
o Specification document: Section 2 of [this document] Hypertext Transfer Protocol (HTTP) Field Name Registry
6. References 6. References
6.1. Normative References 6.1. Normative References
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110, Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022, DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>. <https://www.rfc-editor.org/info/rfc9110>.
skipping to change at page 10, line 16 skipping to change at page 10, line 10
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/info/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
[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/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[STRUCTURED-FIELDS] [STRUCTURED-FIELDS]
Nottingham, M. and P-H. Kamp, "Structured Field Values for Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/info/rfc8941>. <https://www.rfc-editor.org/info/rfc8941>.
6.2. Informative References 6.2. Informative References
[HPACK] Peon, R. and H. Ruellan, "HPACK: Header Compression for [HPACK] Peon, R. and H. Ruellan, "HPACK: Header Compression for
HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
<https://www.rfc-editor.org/info/rfc7541>. <https://www.rfc-editor.org/info/rfc7541>.
[HTTPSIG] Backman, A., Richer, J., and M. Sporny, "HTTP Message [HTTPSIG] Backman, A., Richer, J., and M. Sporny, "HTTP Message
Signatures", draft-ietf-httpbis-message-signatures-16 Signatures", draft-ietf-httpbis-message-signatures-19
(work in progress), February 2023. (work in progress), July 2023.
[QPACK] Krasic, C., Bishop, M., and A. Frindell, Ed., "QPACK: [QPACK] Krasic, C., Bishop, M., and A. Frindell, Ed., "QPACK:
Field Compression for HTTP/3", RFC 9204, Field Compression for HTTP/3", RFC 9204,
DOI 10.17487/RFC9204, June 2022, DOI 10.17487/RFC9204, June 2022,
<https://www.rfc-editor.org/info/rfc9204>. <https://www.rfc-editor.org/info/rfc9204>.
[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/info/rfc6585>. <https://www.rfc-editor.org/info/rfc6585>.
skipping to change at page 11, line 25 skipping to change at page 11, line 21
[TLS] Rescorla, E., "The Transport Layer Security (TLS) Protocol [TLS] 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/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[TLS1.2] Dierks, T. and E. Rescorla, "The Transport Layer Security [TLS1.2] 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/info/rfc5246>. <https://www.rfc-editor.org/info/rfc5246>.
6.3. URIs
[1] https://datatracker.ietf.org/meeting/106/materials/slides-106-
secdispatch-securing-protocols-between-proxies-and-backend-http-
servers-00
[2] https://datatracker.ietf.org/meeting/106/materials/minutes-
106-secdispatch
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 would present the client
intermediate certificate from Figure 1 when establishing a mutually and intermediate certificate from Figure 1 when establishing a
authenticated TLS connection with the TTRP, the proxy would send the mutually authenticated TLS connection with the TTRP, the proxy would
"Client-Cert" field shown in Figure 2 to the backend. Note that line send the Client-Cert field shown in Figure 2 to the backend. Note
breaks and extra spaces have been added to the field value in that line breaks and extra spaces have been added to the field value
Figure 2 and Figure 3 for display and formatting purposes only. in Figures 2 and 3 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 12, line 43 skipping to change at page 12, line 43
MDAxMDkyMTI1NDVaMFYxCzAJBgNVBAYTAlVTMRswGQYDVQQKDBJMZXQncyBBdXRo MDAxMDkyMTI1NDVaMFYxCzAJBgNVBAYTAlVTMRswGQYDVQQKDBJMZXQncyBBdXRo
ZW50aWNhdGUxKjAoBgNVBAMMIUxldCdzIEF1dGhlbnRpY2F0ZSBSb290IEF1dGhv ZW50aWNhdGUxKjAoBgNVBAMMIUxldCdzIEF1dGhlbnRpY2F0ZSBSb290IEF1dGhv
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: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJ Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJ
MZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0 MZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0
yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZ yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZ
Izj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p5Be Izj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p5Be
5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIwADAfBgN 5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIwADAfBgN
VHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMCBsAwEwYDVR0 VHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMCBsAwEwYDVR0
lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1wbGUuY29tMAoGCCq lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1wbGUuY29tMAoGCCq
GSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMjeSkC3dFCOOB8TAiEAx/k GSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMjeSkC3dFCOOB8TAiEAx/k
HSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=: HSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:
Figure 2: Header Field in HTTP Request to Origin Server Figure 2: Header Field in HTTP Request to Origin Server
If the proxy were configured to also include the certificate chain, If the proxy were configured to also include the certificate chain,
it would also include the "Client-Cert-Chain" header field. Note it would also include the Client-Cert-Chain header field. Note that
that while the following example does illustrate the TTRP inserting while the following example does illustrate the TTRP inserting the
the root certificate, many deployments will opt to omit the trust root certificate, many deployments will opt to omit the trust anchor.
anchor.
Client-Cert-Chain: :MIIB5jCCAYugAwIBAgIBFjAKBggqhkjOPQQDAjBWMQsw Client-Cert-Chain: :MIIB5jCCAYugAwIBAgIBFjAKBggqhkjOPQQDAjBWMQsw
CQYDVQQGEwJVUzEbMBkGA1UECgwSTGV0J3MgQXV0aGVudGljYXRlMSowKAYDVQQ CQYDVQQGEwJVUzEbMBkGA1UECgwSTGV0J3MgQXV0aGVudGljYXRlMSowKAYDVQQ
DDCFMZXQncyBBdXRoZW50aWNhdGUgUm9vdCBBdXRob3JpdHkwHhcNMjAwMTE0Mj DDCFMZXQncyBBdXRoZW50aWNhdGUgUm9vdCBBdXRob3JpdHkwHhcNMjAwMTE0Mj
EzMjMwWhcNMzAwMTExMjEzMjMwWjA6MRswGQYDVQQKDBJMZXQncyBBdXRoZW50a EzMjMwWhcNMzAwMTExMjEzMjMwWjA6MRswGQYDVQQKDBJMZXQncyBBdXRoZW50a
WNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTBZMBMGByqGSM49AgEG WNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTBZMBMGByqGSM49AgEG
CCqGSM49AwEHA0IABJf+aA54RC5pyLAR5yfXVYmNpgd+CGUTDp2KOGhc0gK91zx CCqGSM49AwEHA0IABJf+aA54RC5pyLAR5yfXVYmNpgd+CGUTDp2KOGhc0gK91zx
hHesEYkdXkpS2UN8Kati+yHtWCV3kkhCngGyv7RqjZjBkMB0GA1UdDgQWBBRm3W hHesEYkdXkpS2UN8Kati+yHtWCV3kkhCngGyv7RqjZjBkMB0GA1UdDgQWBBRm3W
jLa38lbEYCuiCPct0ZaSED2DAfBgNVHSMEGDAWgBTEA2Q6eecKu9g9yb5glbkhh jLa38lbEYCuiCPct0ZaSED2DAfBgNVHSMEGDAWgBTEA2Q6eecKu9g9yb5glbkhh
VINGDASBgNVHRMBAf8ECDAGAQH/AgEAMA4GA1UdDwEB/wQEAwIBhjAKBggqhkjO VINGDASBgNVHRMBAf8ECDAGAQH/AgEAMA4GA1UdDwEB/wQEAwIBhjAKBggqhkjO
skipping to change at page 14, line 8 skipping to change at page 14, line 8
jAKBggqhkjOPQQDAgNIADBFAiEAmAeg1ycKHriqHnaD4M/UDBpQRpkmdcRFYGMg jAKBggqhkjOPQQDAgNIADBFAiEAmAeg1ycKHriqHnaD4M/UDBpQRpkmdcRFYGMg
1Qyrkx4CIB4ivz3wQcQkGhcsUZ1SOImd/lq1Q0FLf09rGfLQPWDc: 1Qyrkx4CIB4ivz3wQcQkGhcsUZ1SOImd/lq1Q0FLf09rGfLQPWDc:
Figure 3: Certificate Chain in HTTP Request to Origin Server Figure 3: Certificate Chain in HTTP Request to Origin Server
Appendix B. Select Design Considerations Appendix B. Select Design Considerations
B.1. Field Injection B.1. Field Injection
This document requires that the TTRP sanitize the fields of the This document requires that the TTRP sanitize the fields of the
incoming request by removing or overwriting any existing instances of incoming request by removing or overwriting any existing instances of
the "Client-Cert" and "Client-Cert-Chain" header fields before the Client-Cert and Client-Cert-Chain header fields before
dispatching that request to the backend application. Otherwise, a dispatching that request to the backend application. Otherwise, a
client could inject its own values that would appear to the backend client could inject its own values that would appear to the backend
to have come from the TTRP. Although numerous other methods of to have come from the TTRP. Although numerous other methods of
detecting/preventing field injection are possible, such as the use of detecting and preventing field injection are possible, such as the
a unique secret value as part of the field name or value or the use of a unique secret value as part of the field name or value or
application of a signature, HMAC, or AEAD, there is no common general the application of a signature, HMAC, or AEAD, there is no common
mechanism. The potential problem of client field injection is not at general mechanism. The potential problem of client field injection
all unique to the functionality of this document, and it would is not at all unique to the functionality of this document;
therefore be inappropriate for this document to define a one-off therefore, it would be inappropriate for this document to define a
solution. In the absence of a generic common solution existing one-off solution. Since a generic common solution does not currently
currently, stripping/sanitizing the fields is the de facto means of exist, stripping and sanitizing the fields is the de facto means of
protecting against field injection in practice. Sanitizing the protecting against field injection in practice. Sanitizing the
fields is sufficient when properly implemented and is a normative fields is sufficient when properly implemented and is a normative
requirement of Section 4. requirement 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 document could TLS client certificate information of concern to this document could
have been communicated with an extension parameter to the "Forwarded" have been communicated with an extension parameter to the Forwarded
field; however, doing so would have had some disadvantages that this field; however, doing so would have had some disadvantages that this
document endeavored to avoid. The "Forwarded" field syntax allows document endeavored to avoid. The Forwarded field syntax allows for
for information about a full chain of proxied HTTP requests, whereas information about a full chain of proxied HTTP requests, whereas the
the "Client-Cert" and "Client-Cert-Chain" header fields of this Client-Cert and Client-Cert-Chain header fields of this document are
document are concerned only with conveying information about the concerned only with conveying information about the certificate
certificate presented by the originating client on the TLS connection presented by the originating client on the TLS connection to the TTRP
to the TTRP (which appears as the server from that client's (which appears as the server from that client's perspective) to
perspective) to backend applications. The multi-hop syntax of the backend applications. The multi-hop syntax of the Forwarded field is
"Forwarded" field is expressive but also more complicated, which expressive but also more complicated, which would make processing it
would make processing it more cumbersome, and more importantly, make more cumbersome and, more importantly, would make properly sanitizing
properly sanitizing its content as required by Section 4 to prevent its content, as required by Section 4 to prevent field injection,
field injection considerably more difficult and error-prone. Thus, considerably more difficult and error-prone. Thus, this document
this document opted for a flatter and more straightforward structure. opted for a flatter and more straightforward structure.
B.3. The Whole Certificate and Certificate Chain 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 [RFC8705], make use of the Furthermore, some applications, such as that described in [RFC8705],
entire certificate. In order to accommodate the latter and ensure make use of the entire certificate. In order to accommodate the
wide applicability by not trying to cherry-pick particular latter and ensure wide applicability by not trying to cherry-pick
certificate information, this document opted to pass the full, particular certificate information, this document opted to pass the
encoded certificate as the value of the "Client-Cert" field. full, encoded certificate as the value of the Client-Cert field.
The validation of the client certificate and chain of the mutually The validation of the client certificate and chain of the mutually
authenticated TLS connection is typically performed by the TTRP authenticated TLS connection is typically performed by the TTRP
during the handshake. With the responsibility of certificate during the handshake. With the responsibility of certificate
validation falling on the TTRP, the end-entity certificate is validation falling on the TTRP, the end-entity certificate is
oftentimes sufficient for the needs of the origin server. The oftentimes sufficient for the needs of the origin server. The
separate "Client-Cert-Chain" field can convey the certificate chain separate Client-Cert-Chain field can convey the certificate chain for
for origin server deployments that require this additional origin server deployments that require this additional information.
information.
Appendix C. Acknowledgements Acknowledgements
The authors would like to thank the following individuals who've The authors would like to thank the following individuals who have
contributed in various ways ranging from just being generally contributed to this document in various ways, ranging from just being
supportive of bringing forth the document to providing specific generally supportive of bringing forth the document to providing
feedback or content: specific feedback or content:
o Evan Anderson o Evan Anderson
o Annabelle Backman o Annabelle Backman
o Alan Frindell o Alan Frindell
o Rory Hewitt o Rory Hewitt
o Fredrik Jeansson o Fredrik Jeansson
skipping to change at page 16, line 4 skipping to change at page 15, line 50
o Erik Nygren o Erik Nygren
o Mike Ounsworth o Mike Ounsworth
o Lucas Pardue o Lucas Pardue
o Matt Peterson o Matt Peterson
o Eric Rescorla o Eric Rescorla
o Justin Richer
o Justin Richer
o Michael Richardson o Michael Richardson
o Joe Salowey o Joe Salowey
o Rich Salz o Rich Salz
o Mohit Sethi o Mohit Sethi
o Rifaat Shekh-Yusef o Rifaat Shekh-Yusef
skipping to change at page 16, line 28 skipping to change at page 16, line 26
o Nick Sullivan o Nick Sullivan
o Willy Tarreau o Willy Tarreau
o Martin Thomson o Martin Thomson
o Peter Wu o Peter Wu
o Hans Zandbelt o Hans Zandbelt
Appendix D. Document History
To be removed by the RFC Editor before publication as an RFC
draft-ietf-httpbis-client-cert-field-06
o Updates from IESG review
draft-ietf-httpbis-client-cert-field-05
o Correct a couple references
o Updates from Genart Last Call review
o Incorporate AD review feedback
o Editorial updates
draft-ietf-httpbis-client-cert-field-04
o Updates, fixes, and clarifications from WGLC feedback
o State that the certificate chain is in the same order as it
appears in TLS rather than copying the language from TLS
o Update references for HTTP Semantics, HTTP/3, and QPACK to point
to the now RFCs 9110/9114/9204
o HTTP Semantics now a normative ref
o Mention that origin server access control decisions can be
conveyed by selecting response content or with a 403
draft-ietf-httpbis-client-cert-field-02
o Add a note about cert retention on TLS session resumption
o Say to use only the last one in the case of multiple post-
handshake client cert authentications
draft-ietf-httpbis-client-cert-field-01
o Use RFC 8941 Structured Field Values for HTTP
o Introduce a separate header that can convey the certificate chain
o Add considerations on header compression and size
o Describe interaction with caching
o Fill out IANA Considerations with HTTP field name registrations
o Discuss renegotiation
draft-ietf-httpbis-client-cert-field-00
o Initial WG revision
o Mike Bishop added as co-editor
draft-bdc-something-something-certificate-05
o Change intended status of the draft to Informational
o Editorial updates and (hopefully) clarifications
draft-bdc-something-something-certificate-04
o Update reference from draft-ietf-oauth-mtls to RFC8705
draft-bdc-something-something-certificate-03
o Expanded further discussion notes to capture some of the feedback
in and around the presentation of the draft in SECDISPATCH at IETF
107 and add those who've provided such feedback to the
acknowledgements
draft-bdc-something-something-certificate-02
o Editorial tweaks + further discussion notes
draft-bdc-something-something-certificate-01
o Use the RFC v3 Format or die trying
draft-bdc-something-something-certificate-00
o Initial draft after a time constrained and rushed secdispatch
presentation [1] at IETF 106 in Singapore with the recommendation
to write up a draft (at the end of the minutes [2]) and some folks
expressing interest despite the rather poor presentation
Authors' Addresses Authors' Addresses
Brian Campbell Brian Campbell
Ping Identity Ping Identity
Email: bcampbell@pingidentity.com Email: bcampbell@pingidentity.com
Mike Bishop (editor) Mike Bishop (editor)
Akamai Akamai
 End of changes. 68 change blocks. 
274 lines changed or deleted 171 lines changed or added

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