<?xmlversion='1.0' encoding='utf-8'?>version="1.0" encoding="UTF-8"?> <!DOCTYPE rfc [ <!ENTITY nbsp " "> <!ENTITY zwsp "​"> <!ENTITY nbhy "‑"> <!ENTITY wj "⁠"> ]><?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?> <!-- generated by https://github.com/cabo/kramdown-rfc version 1.6.9 (Ruby 2.6.10) --><rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-httpbis-client-cert-field-06"category="info"number="9440" submissionType="IETF" category="info" consensus="true" tocInclude="true" sortRefs="true" symRefs="true" xml:lang="en" updates="" obsoletes="" version="3"><!-- xml2rfc v2v3 conversion 3.15.2 --><front> <title abbrev="Client-Cert Header">Client-Cert HTTP Header Field</title> <seriesInfoname="Internet-Draft" value="draft-ietf-httpbis-client-cert-field-06"/>name="RFC" value="9440"/> <author initials="B." surname="Campbell" fullname="Brian Campbell"> <organization>Ping Identity</organization> <address> <email>bcampbell@pingidentity.com</email> </address> </author> <author initials="M." surname="Bishop" fullname="Mike Bishop" role="editor"> <organization>Akamai</organization> <address> <email>mbishop@evequefou.be</email> </address> </author><date/> <area>Applications and Real-Time</area> <workgroup>HTTP</workgroup><date year="2023" month="July" /> <area>art</area> <workgroup>httpbis</workgroup> <keyword>http</keyword> <keyword>client certificate</keyword> <abstract> <t>This document describes HTTP extension header fields that allow a TLS terminating reverse proxy (TTRP) to convey the client certificate information of a mutually authenticated TLS connection to the origin server in a common and predictable manner.</t> </abstract><note removeInRFC="true"> <name>About This Document</name> <t> Status information for this document may be found at <eref target="https://datatracker.ietf.org/doc/draft-ietf-httpbis-client-cert-field-06/"/>. </t> <t> Discussion of this document takes place on the HTTP Working Group mailing list (<eref target="mailto:ietf-http-wg@w3.org"/>), which is archived at <eref target="https://lists.w3.org/Archives/Public/ietf-http-wg/"/>. Working Group information can be found at <eref target="https://httpwg.org/"/>. </t> <t>Source for this draft and an issue tracker can be found at <eref target="https://github.com/httpwg/http-extensions/labels/client-cert-field"/>.</t> </note></front> <middle> <section anchor="Introduction"> <name>Introduction</name> <t>A fairly common deployment pattern for HTTPS applications is to have the origin HTTP application servers sit behind a reverse proxy that terminates TLS connections from clients. The proxy is accessible to theinternetInternet and dispatches client requests to the appropriate origin server within a private or protected network. The origin servers are not directly accessible by clients and are only reachable through the reverse proxy. The backend details of this type of deployment are typically opaque to clients who make requests to the proxy server and see responses as though they originated from the proxy server itself. Although HTTPS is also usually employed between the proxy and the origin server, the TLS connection that the client establishes for HTTPS is only between itself and the reverse proxy server.</t> <t>The deployment pattern is found in a number of varieties such as n-tier architectures, content delivery networks, applicationload balancingload-balancing services, and ingress controllers.</t> <t>Although not exceedingly prevalent, TLS client certificate authentication is sometimesemployedemployed, and in such cases the origin server often requires information about the client certificate for its application logic. Such logic might include access control decisions, audit logging, and binding issued tokens or cookies to a certificate,andincluding the respective validation of such bindings. The specific details needed from the certificateneededalso vary with the application requirements. In order for these types of application deployments to work in practice, the reverse proxy needs to convey information about the client certificate to the origin application server. At the time of writing, a common way this information is conveyed is by using non-standard fields to carry the certificate (in some encoding) or individual parts thereof in the HTTP request that is dispatched to the origin server. This solutionworksworks, but interoperability between independently developed components can be cumbersome or even impossible depending on the implementation choices respectively made (like what field names are used or are configurable, which parts of the certificate are exposed, or how the certificate is encoded). A well-known predictable approach to this commonly occurring functionality could improve and simplify interoperability between independent implementations.</t> <t>The scope of this document is to describe existing practice while codifying specific details sufficient to facilitate improved and lower-touch interoperability. As such, this document describes two HTTP header fields,<tt>Client-Cert</tt>"Client-Cert" and<tt>Client-Cert-Chain</tt>,"Client-Cert-Chain", which a TLS terminating reverse proxy (TTRP) adds to requests sent to the backend origin servers. The<tt>Client-Cert</tt>Client-Cert field value contains the end-entity client certificate from the mutually authenticated TLS connection between the originating client and the TTRP. Optionally, the<tt>Client-Cert-Chain</tt>Client-Cert-Chain field value contains the certificate chain used for validation of the end-entity certificate. This enables the backend origin server to utilize the client certificate information in its application logic. While there may be additional proxies or hops between the TTRP and the origin server (potentially even with mutually authenticated TLS connections between them), the scope of the<tt>Client-Cert</tt>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.</t> <section anchor="requirements-notation-and-conventions"> <name>Requirements Notation and Conventions</name><t>The<t> The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as described inBCP 14BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they appear in all capitals, as shownhere.</t>here. </t> </section> <section anchor="terminology-and-applicability"> <name>Terminology and Applicability</name> <t>This document uses the following terminology from <xref section="3" sectionFormat="of" target="RFC8941"/> to specify syntax and parsing: List and Byte Sequence.</t> <t>Phrases likeTLS"TLS client certificateauthenticationauthentication" ormutually"mutually authenticatedTLSTLS" are used throughout this document to refer to the process whereby, in addition to the normal TLS server authentication with a certificate, a client presents its X.509 certificate <xref target="RFC5280"/> and proves possession of the corresponding private key to a server when negotiating a TLS connection or the resumption of such a connection. In contemporary versions of TLS <xreftarget="TLS"/>target="RFC8446"/> <xreftarget="TLS1.2"/> thistarget="RFC5246"/>, mutual authentication requiresthatthe client to send the Certificate and CertificateVerify messages during the handshake andforthe server to verify the CertificateVerify and Finished messages.</t> <t>HTTP/2 restricts TLS 1.2 renegotiation (<xref section="9.2.1" sectionFormat="of" target="RFC9113"/>) and prohibits TLS 1.3 post-handshake authentication (<xref section="9.2.3" sectionFormat="of" target="RFC9113"/>). However, they are sometimes used to implement reactive client certificate authentication in HTTP/1.1 <xref target="RFC9112"/> where the server decides whether to request a client certificate based on the HTTP request. HTTP application data sent on such a connection after receipt and verification of the client certificate is also mutually authenticated and thus suitable for the mechanisms described in this document. With post-handshakeauthenticationauthentication, there is also the possibility, though unlikely in practice, of multiple certificates and certificate chains from the client on aconnection, in which caseconnection. In this case, only the certificate and chain of the last post-handshake authentication are to be utilized for the header fields described herein.</t> </section> </section> <section anchor="headers"> <name>HTTP Header Fields and Processing Rules</name> <t>This document designates the following headers, defined further in Sections <xreftarget="header"/>target="header" format="counter"/> and <xreftarget="chain-header"/>target="chain-header" format="counter"/>, respectively, to carry the client certificate information of a mutually authenticated TLS connection. The headers convey the information from the reverse proxy to the origin server.</t><dl><dl spacing="normal" newline="true"> <dt>Client-Cert:</dt><dd> <t>The<dd>The end-entity certificate used by the client in the TLS handshake with the reverseproxy.</t>proxy. </dd> <dt>Client-Cert-Chain:</dt><dd> <t>The<dd>The certificate chain used for validation of the end-entity certificate provided by the client in the TLS handshake with the reverseproxy.</t> </dd>proxy.</dd> </dl> <section anchor="encoding"> <name>Encoding</name> <t>The headers in this document encode certificates as Byte Sequences (<xref section="3.3.5" sectionFormat="of" target="RFC8941"/>) where the value of the binary data is aDER encodedDER-encoded <xreftarget="ITU.X690.1994"/>target="ITU.X690"/> X.509 certificate <xref target="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.</t> <t>Note that certificates are often storedencodedinaan encoded textual format, such as the one described in <xref section="5.1" sectionFormat="of" target="RFC7468"/>, which is already nearly compatible with a ByteSequence; if so,Sequence. If certificates are encoded as such, it will be sufficient to replace<tt>---(BEGIN|END) CERTIFICATE---</tt>"---(BEGIN|END) CERTIFICATE---" with<tt>:</tt>":" and remove line breaks in order to generate an appropriate item.</t> </section> <section anchor="header"> <name>Client-Cert HTTP Header Field</name> <t>In the context of a TLS terminating reverse proxy deployment, the proxy makes the TLS client certificate available to the backend application with the Client-Cert HTTP header field. This field contains the end-entity certificate used by the client in the TLS handshake.</t> <t>Client-Cert is a Byte Sequence with the value of the header encoded as described in <xref target="encoding"/>.</t> <t>The<tt>Client-Cert</tt>Client-Cert header field is only for use in HTTP requests and <bcp14>MUST NOT</bcp14> be used in HTTP responses. It is a singleton header field value as defined in <xref section="5.5" sectionFormat="of" target="RFC9110"/>, which <bcp14>MUST NOT</bcp14> have a list of values or occur multiple times in a request.</t> <t><xref target="example-header"/> in <xref target="example"/> has an example of the<tt>Client-Cert</tt>Client-Cert header field.</t> </section> <section anchor="chain-header"> <name>Client-Cert-Chain HTTP Header Field</name> <t>In the context of a TLS terminating reverse proxy deployment, the proxy <bcp14>MAY</bcp14> make the certificate chain available to the backend application with the Client-Cert-Chain HTTP header field.</t> <t>Client-Cert-Chain is a List (<xref section="3.1" sectionFormat="of" target="RFC8941"/>). Each item in thelistList <bcp14>MUST</bcp14> be a Byte Sequence encoded as described in <xref target="encoding"/>. The order is the same as the ordering in TLS(such as(as described in <xref section="4.4.2" sectionFormat="of"target="TLS"/>).</t>target="RFC8446"/>).</t> <t>Client-Cert-Chain <bcp14>MUST NOT</bcp14> appear unless Client-Cert is also present, and it does not itself include the end-entity certificate that is already present in Client-Cert. The root certificate <bcp14>MAY</bcp14> be omitted from Client-Cert-Chain, provided that the target origin server is known to possess the omitted trust anchor.</t> <t>The<tt>Client-Cert-Chain</tt>Client-Cert-Chain header field is only for use in HTTP requests and <bcp14>MUST NOT</bcp14> be used in HTTP responses. It <bcp14>MAY</bcp14> 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.</t> <t><xref target="example-chain-header"/> in <xref target="example"/> has an example of the<tt>Client-Cert-Chain</tt>Client-Cert-Chain header field.</t> </section> <section anchor="processing-rules"> <name>Processing Rules</name> <t>This section outlines the applicable processing rules for aTLS terminating reverse proxy (TTRP)TTRP that has negotiated a mutually authenticated TLS connection to convey the client certificate from that connection to the backend origin servers.Use of theThis technique is to be used as a configuration or deploymentoptionoption, and the processing rules described herein are for servers operating with that option enabled.</t> <t>A TTRP negotiates the use of a mutually authenticated TLS connection with the client, such as is described in <xreftarget="TLS"/>target="RFC8446"/> or <xreftarget="TLS1.2"/>,target="RFC5246"/>, and validates the client certificate per its policy and trusted certificate authorities. Each HTTP request on the underlying TLS connection is dispatched to the origin server with the following modifications:</t> <ol spacing="normal"type="1"><li>Thetype="1"> <li>The client certificate is placed in the<tt>Client-Cert</tt>Client-Cert header field of the dispatched request, as described in <xref target="header"/>.</li> <li>If so configured, the validation chain of the client certificate is placed in the<tt>Client-Cert-Chain</tt>Client-Cert-Chain header field of the request, as described in <xref target="chain-header"/>.</li> <li>Any occurrence of the<tt>Client-Cert</tt>Client-Cert or<tt>Client-Cert-Chain</tt>Client-Cert-Chain header fields in the original incoming request <bcp14>MUST</bcp14> be removed or overwritten before forwarding the request. An incoming request that has a<tt>Client-Cert</tt>Client-Cert or<tt>Client-Cert-Chain</tt>Client-Cert-Chain header field <bcp14>MAY</bcp14> be rejected with an HTTP 400 response.</li> </ol> <t>Requests to the TTRP made over a TLS connection where the use of client certificate authentication was not negotiated <bcp14>MUST</bcp14> be sanitized by removing any and all occurrences of the<tt>Client-Cert</tt>Client-Cert and<tt>Client-Cert-Chain</tt>Client-Cert-Chain header fields prior to dispatching the request to the backend server.</t> <t>Backend origin servers may then use the<tt>Client-Cert</tt>Client-Cert header field of the request to determine if the connection from the client to the TTRP was mutually authenticated and, if so, the certificate thereby presented by the client. Access control decisions based on the client certificate (or lack thereof) can be conveyed by selecting response content as appropriate or with an HTTP 403 response, if the certificate is deemed unacceptable for the given context. Note that TLS clients that rely on error indications at the TLS layer for an unacceptable certificate will not receive those signals.</t> <t>When the value of the<tt>Client-Cert</tt>Client-Cert request header field is used to select a response (e.g., the response content is access-controlled), the response <bcp14>MUST</bcp14> either be uncacheable (e.g., by sending<tt>Cache-Control: no-store</tt>)Cache-Control: no-store) or be designated for selective reuse only for subsequent requests with the same<tt>Client-Cert</tt>Client-Cert header field value by sending a<tt>Vary: Client-Cert</tt>"Vary: Client-Cert" response header. If a TTRP encounters a response witha <tt>client-cert</tt> field nameClient-Cert or Client-Cert-Chain in the<tt>Vary</tt>Vary headerfield,field (<xref section="12.5.5" sectionFormat="of" target="RFC9110"/>), it <bcp14>SHOULD</bcp14> prevent the user agent from caching the response by transforming the value of the<tt>Vary</tt>Vary response header field to<tt>*</tt>.</t>"*".</t> <t>Forward proxies and other intermediaries <bcp14>MUST NOT</bcp14> add the<tt>Client-Cert</tt>Client-Cert or<tt>Client-Cert-Chain</tt>Client-Cert-Chain header fields torequests,requests or modify an existing<tt>Client-Cert</tt>Client-Cert or<tt>Client-Cert-Chain</tt>Client-Cert-Chain header field. Similarly, clients <bcp14>MUST NOT</bcp14> employ the<tt>Client-Cert</tt>Client-Cert or<tt>Client-Cert-Chain</tt>Client-Cert-Chain header field in requests.</t> </section> </section> <section anchor="deployment"> <name>Deployment Considerations</name> <section anchor="header-field-compression"> <name>Header Field Compression</name> <t>If the connection between the TTRP and origin is capable of field compression (e.g., HPACK <xreftarget="HPACK"/>target="RFC7541"/> or QPACK <xreftarget="QPACK"/>),target="RFC9204"/>), and the TTRP multiplexes more than one client's requests into that connection, the size and variation of<tt>Client-Cert</tt>Client-Cert and<tt>Client-Cert-Chain</tt>Client-Cert-Chain field values can reduce compression efficiency significantly. An origin could mitigate the efficiency loss by increasing the size of the dynamic table. If the TTRP determines that the origin dynamic table is not sufficiently large, it may find it beneficial to always send the field value as aliteral,literal rather than entering it into the table.</t> </section> <section anchor="message-header-size"> <name>Message Header Size</name> <t>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 code per <xref section="5" sectionFormat="of" target="RFC6585"/>. Due to the typical size of the field values containing certificate data, recipients may need to be configured to allow for a larger maximum header size. An intermediary generating client certificate header fields on connections that allow for advertising the maximum acceptable header size (e.g., HTTP/2 <xref target="RFC9113"/> or HTTP/3 <xref target="RFC9114"/>) should account for the additional size of the header of the requests itsends vs.sends, versus the requests itreceivesreceives, by advertising a value to its clients that is sufficiently smaller so as to allow for the addition of certificate data.</t> </section> <section anchor="tls-session-resumption"> <name>TLS Session Resumption</name> <t>Some TLS implementations do not retain client certificate information when resuming. Providing inconsistent values of Client-Cert and Client-Cert-Chain when resuming might lead to errors, so implementations that are unable to provide these values <bcp14>SHOULD</bcp14> either disable resumption for connections with client certificates or initially omit a<tt>Client-Cert</tt>Client-Cert or<tt>Client-Cert-Chain</tt>Client-Cert-Chain field if it might not be available after resuming.</t> </section> </section> <section anchor="sec"> <name>Security Considerations</name> <t>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.UseHowever, use of the header fields outside that intended usecase, however,case may undermine the protections afforded by TLS client certificate authentication. Therefore, steps such as those described below need to be taken to prevent unintended use, both in sending the header field and in relying on its value.</t> <t>Producing and consuming the<tt>Client-Cert</tt>Client-Cert and<tt>Client-Cert-Chain</tt>Client-Cert-Chain header fields <bcp14>SHOULD</bcp14> be configurable options, respectively, in a TTRP and backend server (or in an 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.</t> <t>In order to prevent field injection, backend servers <bcp14>MUST</bcp14> only accept the<tt>Client-Cert</tt>Client-Cert and<tt>Client-Cert-Chain</tt>Client-Cert-Chain header fields from a trusted TTRP (or other proxy in a trusted path from the TTRP). A TTRP <bcp14>MUST</bcp14> 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.</t> <t>The communication between a TTRP and backend server needs to be secured against eavesdropping and modification by unintended parties.</t> <t>The configuration options and request sanitization are necessaryfunctionalityfunctionalities of the respective servers. The other requirements can be met in a number of ways, which will vary based on specific deployments. The communication between a TTRP and backend or origin server, for example, might be authenticated in some way with the insertion and consumption of the<tt>Client-Cert</tt>Client-Cert and<tt>Client-Cert-Chain</tt>Client-Cert-Chain header fields occurring only on that connection. <xref section="B.3" sectionFormat="of" target="I-D.ietf-httpbis-message-signatures"/> gives one example of this with an application of HTTP Message Signatures. Alternatively, the network topology might dictate a private network such that the backend application is only able to accept requests from the TTRP and the proxy can only make requests to that server. Other deployments that meet the requirements set forth herein are also possible.</t> </section> <section anchor="iana-considerations"> <name>IANA Considerations</name> <section anchor="http-field-name-registrations"> <name>HTTP Field Name Registrations</name><t>Please register<t>IANA has registered the following entries in the "Hypertext Transfer Protocol (HTTP) Field Name Registry" defined byHTTP Semantics"HTTP Semantics" <xref target="RFC9110"/>:</t><ul spacing="normal"> <li>Field name: Client-Cert</li> <li>Status: permanent</li> <li>Specification document: <xref target="headers"/> of [this document] <br/></li> <li>Field name: Client-Cert-Chain</li> <li>Status: permanent</li> <li>Specification document: <xref target="headers"/> of [this document]</li> </ul><table anchor="table_1"> <name>Hypertext Transfer Protocol (HTTP) Field Name Registry</name> <thead> <tr> <th>Field Name</th> <th>Status</th> <th>Reference</th> </tr> </thead> <tbody> <tr> <td>Client-Cert</td> <td>permanent</td> <td>RFC 9440, <xref target="headers"/></td> </tr> <tr> <td>Client-Cert-Chain</td> <td>permanent</td> <td>RFC 9440, <xref target="headers"/></td> </tr> </tbody> </table> </section> </section> </middle> <back> <displayreference target="RFC8941" to="STRUCTURED-FIELDS"/> <displayreference target="RFC9110" to="HTTP"/> <displayreference target="RFC9112" to="HTTP/1.1"/> <displayreference target="RFC9113" to="HTTP/2"/> <displayreference target="RFC9114" to="HTTP/3"/> <displayreference target="I-D.ietf-httpbis-message-signatures" to="HTTPSIG"/> <displayreference target="RFC8446" to="TLS"/> <displayreference target="RFC9204" to="QPACK"/> <displayreference target="RFC7541" to="HPACK"/> <displayreference target="RFC5246" to="TLS1.2"/> <references> <name>References</name> <references> <name>Normative References</name> <!-- [RFC8941] [STRUCTURED-FIELDS] updated to long version because xi:include shows Kamp's name as "P. Kamp" instead of "P-H. Kamp"--> <reference anchor="RFC8941"> <front> <title>Structured Field Values for HTTP</title> <author fullname="M. Nottingham" initials="M."surname="Nottingham"> <organization/> </author>surname="Nottingham"/> <author fullname="P-H. Kamp" initials="P-H."surname="Kamp"> <organization/> </author>surname="Kamp"/> <date month="February" year="2021"/><abstract> <t>This document describes a set of data types and associated algorithms that are intended to make it easier and safer to define and handle HTTP header and trailer fields, known as "Structured Fields", "Structured Headers", or "Structured Trailers". It is intended for use by specifications of new HTTP fields that wish to use a common syntax that is more restrictive than traditional HTTP field values.</t> </abstract></front> <seriesInfo name="RFC" value="8941"/> <seriesInfo name="DOI" value="10.17487/RFC8941"/> </reference> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9110.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5280.xml"/> <referenceanchor="RFC9110"> <front> <title>HTTP Semantics</title> <author fullname="R. Fielding" initials="R." role="editor" surname="Fielding"> <organization/> </author> <author fullname="M. Nottingham" initials="M." role="editor" surname="Nottingham"> <organization/> </author> <author fullname="J. Reschke" initials="J." role="editor" surname="Reschke"> <organization/> </author> <date month="June" year="2022"/> <abstract> <t>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. </t> <t>This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230.</t> </abstract> </front> <seriesInfo name="STD" value="97"/> <seriesInfo name="RFC" value="9110"/> <seriesInfo name="DOI" value="10.17487/RFC9110"/> </reference> <reference anchor="RFC2119"> <front> <title>Key words for use in RFCs to Indicate Requirement Levels</title> <author fullname="S. Bradner" initials="S." surname="Bradner"> <organization/> </author> <date month="March" year="1997"/> <abstract> <t>In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t> </abstract> </front> <seriesInfo name="BCP" value="14"/> <seriesInfo name="RFC" value="2119"/> <seriesInfo name="DOI" value="10.17487/RFC2119"/> </reference> <reference anchor="RFC8174"> <front> <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title> <author fullname="B. Leiba" initials="B." surname="Leiba"> <organization/> </author> <date month="May" year="2017"/> <abstract> <t>RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t> </abstract> </front> <seriesInfo name="BCP" value="14"/> <seriesInfo name="RFC" value="8174"/> <seriesInfo name="DOI" value="10.17487/RFC8174"/> </reference> <reference anchor="RFC5280"> <front> <title>Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile</title> <author fullname="D. Cooper" initials="D." surname="Cooper"> <organization/> </author> <author fullname="S. Santesson" initials="S." surname="Santesson"> <organization/> </author> <author fullname="S. Farrell" initials="S." surname="Farrell"> <organization/> </author> <author fullname="S. Boeyen" initials="S." surname="Boeyen"> <organization/> </author> <author fullname="R. Housley" initials="R." surname="Housley"> <organization/> </author> <author fullname="W. Polk" initials="W." surname="Polk"> <organization/> </author> <date month="May" year="2008"/> <abstract> <t>This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfo name="RFC" value="5280"/> <seriesInfo name="DOI" value="10.17487/RFC5280"/> </reference> <reference anchor="ITU.X690.1994">anchor="ITU.X690" target="https://www.itu.int/rec/T-REC-X.690/en"> <front> <title>InformationTechnologytechnology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)</title> <author><organization>International Telecommunications Union</organization><organization>ITU-T</organization> </author> <dateyear="1994"/>month="February" year="2021"/> </front> <seriesInfoname="ITU-T" value="Recommendation X.690"/>name="ITU-T Recommendation" value="X.690"/> </reference> </references> <references> <name>Informative References</name><reference anchor="RFC9112"> <front> <title>HTTP/1.1</title> <author fullname="R. Fielding" initials="R." role="editor" surname="Fielding"> <organization/> </author> <author fullname="M. Nottingham" initials="M." role="editor" surname="Nottingham"> <organization/> </author> <author fullname="J. Reschke" initials="J." role="editor" surname="Reschke"> <organization/> </author> <date month="June" year="2022"/> <abstract> <t>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document specifies the HTTP/1.1 message syntax, message parsing, connection management, and related security concerns. </t> <t>This document obsoletes portions of RFC 7230.</t> </abstract> </front> <seriesInfo name="STD" value="99"/> <seriesInfo name="RFC" value="9112"/> <seriesInfo name="DOI" value="10.17487/RFC9112"/> </reference> <reference anchor="RFC9113"> <front> <title>HTTP/2</title> <author fullname="M. Thomson" initials="M." role="editor" surname="Thomson"> <organization/> </author> <author fullname="C. Benfield" initials="C." role="editor" surname="Benfield"> <organization/> </author> <date month="June" year="2022"/> <abstract> <t>This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP), referred<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9112.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9113.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9114.xml"/> <!-- [I-D.ietf-httpbis-message-signatures] IESG Evaluation::Revised I-D Needed. Updated toas HTTPlong version2 (HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduced latency by introducing field compression and allowing multiple concurrent exchanges on the same connection.</t> <t>This document obsoletes RFCs 7540 and 8740.</t> </abstract> </front> <seriesInfo name="RFC" value="9113"/> <seriesInfo name="DOI" value="10.17487/RFC9113"/> </reference> <reference anchor="RFC9114"> <front> <title>HTTP/3</title> <author fullname="M. Bishop" initials="M." role="editor" surname="Bishop"> <organization/> </author> <date month="June" year="2022"/> <abstract> <t>The QUIC transport protocol has several features that are desirable in a transportbecause missing editor roles forHTTP, such as stream multiplexing, per-stream flow control,Backman andlow-latency connection establishment. This document describes a mapping of HTTP semantics over QUIC. This document also identifies HTTP/2 features that are subsumed by QUIC and describes how HTTP/2 extensions can be ported to HTTP/3.</t> </abstract> </front> <seriesInfo name="RFC" value="9114"/> <seriesInfo name="DOI" value="10.17487/RFC9114"/> </reference>Richer. --> <referenceanchor="I-D.ietf-httpbis-message-signatures">anchor="I-D.ietf-httpbis-message-signatures" target="https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-message-signatures-17"> <front> <title>HTTP Message Signatures</title> <author initials="A." surname="Backman" fullname="Annabelle Backman"initials="A." surname="Backman">role="editor"> <organization>Amazon</organization> </author> <author initials="J." surname="Richer" fullname="Justin Richer"initials="J." surname="Richer">role="editor"> <organization>Bespoke Engineering</organization> </author> <authorfullname="Manu Sporny"initials="M."surname="Sporny">surname="Sporny" fullname="Manu Sporny"> <organization>Digital Bazaar</organization> </author> <dateday="6" month="February"month="May" day="2" year="2023"/><abstract> <t> This document describes a mechanism for creating, encoding, and verifying digital signatures or message authentication codes over components of an HTTP message. This mechanism supports use cases where the full HTTP message may not be known to the signer, and where the message may be transformed (e.g., by intermediaries) before reaching the verifier. This document also describes a means for requesting that a signature be applied to a subsequent HTTP message in an ongoing HTTP exchange. </t> </abstract></front> <seriesInfo name="Internet-Draft"value="draft-ietf-httpbis-message-signatures-16"/> </reference> <reference anchor="TLS"> <front> <title>The Transport Layer Security (TLS) Protocol Version 1.3</title> <author fullname="E. Rescorla" initials="E." surname="Rescorla"> <organization/> </author> <date month="August" year="2018"/> <abstract> <t>This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery.</t> <t>This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations.</t> </abstract> </front> <seriesInfo name="RFC" value="8446"/> <seriesInfo name="DOI" value="10.17487/RFC8446"/> </reference> <reference anchor="TLS1.2"> <front> <title>The Transport Layer Security (TLS) Protocol Version 1.2</title> <author fullname="T. Dierks" initials="T." surname="Dierks"> <organization/> </author> <author fullname="E. Rescorla" initials="E." surname="Rescorla"> <organization/> </author> <date month="August" year="2008"/> <abstract> <t>This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfo name="RFC" value="5246"/> <seriesInfo name="DOI" value="10.17487/RFC5246"/> </reference> <reference anchor="RFC7468"> <front> <title>Textual Encodings of PKIX, PKCS, and CMS Structures</title> <author fullname="S. Josefsson" initials="S." surname="Josefsson"> <organization/> </author> <author fullname="S. Leonard" initials="S." surname="Leonard"> <organization/> </author> <date month="April" year="2015"/> <abstract> <t>This document describes and discusses the textual encodings of the Public-Key Infrastructure X.509 (PKIX), Public-Key Cryptography Standards (PKCS), and Cryptographic Message Syntax (CMS). The textual encodings are well-known, are implemented by several applications and libraries, and are widely deployed. This document articulates the de facto rules by which existing implementations operate and defines them so that future implementations can interoperate.</t> </abstract> </front> <seriesInfo name="RFC" value="7468"/> <seriesInfo name="DOI" value="10.17487/RFC7468"/> </reference> <reference anchor="HPACK"> <front> <title>HPACK: Header Compression for HTTP/2</title> <author fullname="R. Peon" initials="R." surname="Peon"> <organization/> </author> <author fullname="H. Ruellan" initials="H." surname="Ruellan"> <organization/> </author> <date month="May" year="2015"/> <abstract> <t>This specification defines HPACK, a compression format for efficiently representing HTTP header fields, to be used in HTTP/2.</t> </abstract> </front> <seriesInfo name="RFC" value="7541"/> <seriesInfo name="DOI" value="10.17487/RFC7541"/> </reference> <reference anchor="QPACK"> <front> <title>QPACK: Field Compression for HTTP/3</title> <author fullname="C. Krasic" initials="C." surname="Krasic"> <organization/> </author> <author fullname="M. Bishop" initials="M." surname="Bishop"> <organization/> </author> <author fullname="A. Frindell" initials="A." role="editor" surname="Frindell"> <organization/> </author> <date month="June" year="2022"/> <abstract> <t>This specification defines QPACK: a compression format for efficiently representing HTTP fields that is to be used in HTTP/3. This is a variation of HPACK compression that seeks to reduce head-of-line blocking.</t> </abstract> </front> <seriesInfo name="RFC" value="9204"/> <seriesInfo name="DOI" value="10.17487/RFC9204"/> </reference> <reference anchor="RFC6585"> <front> <title>Additional HTTP Status Codes</title> <author fullname="M. Nottingham" initials="M." surname="Nottingham"> <organization/> </author> <author fullname="R. Fielding" initials="R." surname="Fielding"> <organization/> </author> <date month="April" year="2012"/> <abstract> <t>This document specifies additional HyperText Transfer Protocol (HTTP) status codes for a variety of common situations. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfo name="RFC" value="6585"/> <seriesInfo name="DOI" value="10.17487/RFC6585"/> </reference> <reference anchor="RFC7239"> <front> <title>Forwarded HTTP Extension</title> <author fullname="A. Petersson" initials="A." surname="Petersson"> <organization/> </author> <author fullname="M. Nilsson" initials="M." surname="Nilsson"> <organization/> </author> <date month="June" year="2014"/> <abstract> <t>This document defines an HTTP extension header field that allows proxy components to disclose information lost in the proxying process, for example, the originating IP address of a request or IP address of the proxy on the user-agent-facing interface. In a path of proxying components, this makes it possible to arrange it so that each subsequent component will have access to, for example, all IP addresses used in the chain of proxied HTTP requests.</t> <t>This document also specifies guidelines for a proxy administrator to anonymize the origin of a request.</t> </abstract> </front> <seriesInfo name="RFC" value="7239"/> <seriesInfo name="DOI" value="10.17487/RFC7239"/> </reference> <reference anchor="RFC8705"> <front> <title>OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens</title> <author fullname="B. Campbell" initials="B." surname="Campbell"> <organization/> </author> <author fullname="J. Bradley" initials="J." surname="Bradley"> <organization/> </author> <author fullname="N. Sakimura" initials="N." surname="Sakimura"> <organization/> </author> <author fullname="T. Lodderstedt" initials="T." surname="Lodderstedt"> <organization/> </author> <date month="February" year="2020"/> <abstract> <t>This document describes OAuth client authentication and certificate-bound access and refresh tokens using mutual Transport Layer Security (TLS) authentication with X.509 certificates. OAuth clients are provided a mechanism for authentication to the authorization server using mutual TLS, based on either self-signed certificates or public key infrastructure (PKI). OAuth authorization servers are provided a mechanism for binding access tokens to a client's mutual-TLS certificate, and OAuth protected resources are provided a method for ensuring that such an access token presented to it was issued to the client presenting the token.</t> </abstract> </front> <seriesInfo name="RFC" value="8705"/> <seriesInfo name="DOI" value="10.17487/RFC8705"/>value="draft-ietf-httpbis-message-signatures-17"/> </reference> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8446.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5246.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7468.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7541.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9204.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6585.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7239.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8705.xml"/> </references> </references> <section anchor="example"> <name>Example</name> <t>In a hypothetical example where a TLS clientpresentswould present the client and intermediate certificate from <xref target="example-chain"/> when establishing a mutually authenticated TLS connection with the TTRP, the proxy would send the<tt>Client-Cert</tt>Client-Cert field shown in <xref target="example-header"/> to the backend. Note that line breaks and extra spaces have been added to the field value in Figures <xreftarget="example-header"/>target="example-header" format="counter"/> and <xreftarget="example-chain-header"/>target="example-chain-header" format="counter"/> for display and formatting purposes only.</t> <figure anchor="example-chain"> <name>Certificate Chain (withclient certificate first)</name> <artwork><![CDATA[Client Certificate First)</name> <sourcecode><![CDATA[ -----BEGIN CERTIFICATE----- MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJMZXQncyBB dXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0yMDAx MTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZI zj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p 5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIw ADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMC BsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1w bGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMje SkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk= -----END CERTIFICATE----- -----BEGIN CERTIFICATE----- MIIB5jCCAYugAwIBAgIBFjAKBggqhkjOPQQDAjBWMQswCQYDVQQGEwJVUzEbMBkG A1UECgwSTGV0J3MgQXV0aGVudGljYXRlMSowKAYDVQQDDCFMZXQncyBBdXRoZW50 aWNhdGUgUm9vdCBBdXRob3JpdHkwHhcNMjAwMTE0MjEzMjMwWhcNMzAwMTExMjEz MjMwWjA6MRswGQYDVQQKDBJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxB IEludGVybWVkaWF0ZSBDQTBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABJf+aA54 RC5pyLAR5yfXVYmNpgd+CGUTDp2KOGhc0gK91zxhHesEYkdXkpS2UN8Kati+yHtW CV3kkhCngGyv7RqjZjBkMB0GA1UdDgQWBBRm3WjLa38lbEYCuiCPct0ZaSED2DAf BgNVHSMEGDAWgBTEA2Q6eecKu9g9yb5glbkhhVINGDASBgNVHRMBAf8ECDAGAQH/ AgEAMA4GA1UdDwEB/wQEAwIBhjAKBggqhkjOPQQDAgNJADBGAiEA5pLvaFwRRkxo mIAtDIwg9D7gC1xzxBl4r28EzmSO1pcCIQCJUShpSXO9HDIQMUgH69fNDEMHXD3R RX5gP7kuu2KGMg== -----END CERTIFICATE----- -----BEGIN CERTIFICATE----- MIICBjCCAaygAwIBAgIJAKS0yiqKtlhoMAoGCCqGSM49BAMCMFYxCzAJBgNVBAYT AlVTMRswGQYDVQQKDBJMZXQncyBBdXRoZW50aWNhdGUxKjAoBgNVBAMMIUxldCdz IEF1dGhlbnRpY2F0ZSBSb290IEF1dGhvcml0eTAeFw0yMDAxMTQyMTI1NDVaFw00 MDAxMDkyMTI1NDVaMFYxCzAJBgNVBAYTAlVTMRswGQYDVQQKDBJMZXQncyBBdXRo ZW50aWNhdGUxKjAoBgNVBAMMIUxldCdzIEF1dGhlbnRpY2F0ZSBSb290IEF1dGhv cml0eTBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABFoaHU+Z5bPKmGzlYXtCf+E6 HYj62fORaHDOrt+yyh3H/rTcs7ynFfGn+gyFsrSP3Ez88rajv+U2NfD0o0uZ4Pmj YzBhMB0GA1UdDgQWBBTEA2Q6eecKu9g9yb5glbkhhVINGDAfBgNVHSMEGDAWgBTE A2Q6eecKu9g9yb5glbkhhVINGDAPBgNVHRMBAf8EBTADAQH/MA4GA1UdDwEB/wQE AwIBhjAKBggqhkjOPQQDAgNIADBFAiEAmAeg1ycKHriqHnaD4M/UDBpQRpkmdcRF YGMg1Qyrkx4CIB4ivz3wQcQkGhcsUZ1SOImd/lq1Q0FLf09rGfLQPWDc -----END CERTIFICATE-----]]></artwork>]]></sourcecode> </figure> <figure anchor="example-header"> <name>Header Field in HTTP Request to Origin Server</name><artwork><![CDATA[<sourcecode><![CDATA[ Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJ MZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0 yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZ Izj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p5Be 5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIwADAfBgN VHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMCBsAwEwYDVR0 lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1wbGUuY29tMAoGCCq GSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMjeSkC3dFCOOB8TAiEAx/k HSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:]]></artwork>]]></sourcecode> </figure> <t>If the proxy were configured to also include the certificate chain, it would also include the<tt>Client-Cert-Chain</tt>Client-Cert-Chain header field. Note that while the following example does illustrate the TTRP inserting the root certificate, many deployments will opt to omit the trust anchor.</t> <figure anchor="example-chain-header"> <name>Certificate Chain in HTTP Request to Origin Server</name><artwork><![CDATA[<sourcecode><![CDATA[ Client-Cert-Chain: :MIIB5jCCAYugAwIBAgIBFjAKBggqhkjOPQQDAjBWMQsw CQYDVQQGEwJVUzEbMBkGA1UECgwSTGV0J3MgQXV0aGVudGljYXRlMSowKAYDVQQ DDCFMZXQncyBBdXRoZW50aWNhdGUgUm9vdCBBdXRob3JpdHkwHhcNMjAwMTE0Mj EzMjMwWhcNMzAwMTExMjEzMjMwWjA6MRswGQYDVQQKDBJMZXQncyBBdXRoZW50a WNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTBZMBMGByqGSM49AgEG CCqGSM49AwEHA0IABJf+aA54RC5pyLAR5yfXVYmNpgd+CGUTDp2KOGhc0gK91zx hHesEYkdXkpS2UN8Kati+yHtWCV3kkhCngGyv7RqjZjBkMB0GA1UdDgQWBBRm3W jLa38lbEYCuiCPct0ZaSED2DAfBgNVHSMEGDAWgBTEA2Q6eecKu9g9yb5glbkhh VINGDASBgNVHRMBAf8ECDAGAQH/AgEAMA4GA1UdDwEB/wQEAwIBhjAKBggqhkjO PQQDAgNJADBGAiEA5pLvaFwRRkxomIAtDIwg9D7gC1xzxBl4r28EzmSO1pcCIQC JUShpSXO9HDIQMUgH69fNDEMHXD3RRX5gP7kuu2KGMg==:, :MIICBjCCAaygAw IBAgIJAKS0yiqKtlhoMAoGCCqGSM49BAMCMFYxCzAJBgNVBAYTAlVTMRswGQYDV QQKDBJMZXQncyBBdXRoZW50aWNhdGUxKjAoBgNVBAMMIUxldCdzIEF1dGhlbnRp Y2F0ZSBSb290IEF1dGhvcml0eTAeFw0yMDAxMTQyMTI1NDVaFw00MDAxMDkyMTI 1NDVaMFYxCzAJBgNVBAYTAlVTMRswGQYDVQQKDBJMZXQncyBBdXRoZW50aWNhdG UxKjAoBgNVBAMMIUxldCdzIEF1dGhlbnRpY2F0ZSBSb290IEF1dGhvcml0eTBZM BMGByqGSM49AgEGCCqGSM49AwEHA0IABFoaHU+Z5bPKmGzlYXtCf+E6HYj62fOR aHDOrt+yyh3H/rTcs7ynFfGn+gyFsrSP3Ez88rajv+U2NfD0o0uZ4PmjYzBhMB0 GA1UdDgQWBBTEA2Q6eecKu9g9yb5glbkhhVINGDAfBgNVHSMEGDAWgBTEA2Q6ee cKu9g9yb5glbkhhVINGDAPBgNVHRMBAf8EBTADAQH/MA4GA1UdDwEB/wQEAwIBh jAKBggqhkjOPQQDAgNIADBFAiEAmAeg1ycKHriqHnaD4M/UDBpQRpkmdcRFYGMg 1Qyrkx4CIB4ivz3wQcQkGhcsUZ1SOImd/lq1Q0FLf09rGfLQPWDc:]]></artwork>]]></sourcecode> </figure> </section> <section anchor="select-design-considerations"> <name>Select Design Considerations</name> <section anchor="field-injection"> <name>Field Injection</name> <t>This document requires that the TTRP sanitize the fields of the incoming request by removing or overwriting any existing instances of the<tt>Client-Cert</tt>Client-Cert and<tt>Client-Cert-Chain</tt>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 ofdetecting/preventingdetecting and preventing field injection are possible, such as the use of a unique secret value as part of the field name or value or the application of a signature, HMAC, or AEAD, there is no common general mechanism. The potential problem of client field injection is not at all unique to the functionality of thisdocument, anddocument; therefore, it wouldthereforebe inappropriate for this document to define a one-off solution.In the absence ofSince a generic common solutionexisting currently, stripping/sanitizingdoes not currently exist, stripping and sanitizing the fields is the de facto means of protecting against field injection in practice. Sanitizing the fields is sufficient when properly implemented and is a normative requirement of <xref target="sec"/>.</t> </section> <section anchor="the-forwarded-http-extension"> <name>The Forwarded HTTP Extension</name> <t>The<tt>Forwarded</tt>Forwarded HTTP header field defined in <xref target="RFC7239"/> allows proxy components to disclose information lost in the proxying process. The TLS client certificate information of concern to this document could have been communicated with an extension parameter to the<tt>Forwarded</tt>Forwarded field; however, doing so would have had some disadvantages that this document endeavored to avoid. The<tt>Forwarded</tt>Forwarded field syntax allows for information about a full chain of proxied HTTP requests, whereas the<tt>Client-Cert</tt>Client-Cert and<tt>Client-Cert-Chain</tt>Client-Cert-Chain header fields of this document are concerned only with conveying information about the certificate presented by the originating client on the TLS connection to the TTRP (which appears as the server from that client's perspective) to backend applications. The multi-hop syntax of the<tt>Forwarded</tt>Forwarded field is expressive but also more complicated, which would make processing it morecumbersome, andcumbersome and, more importantly, would make properly sanitizing itscontentcontent, as required by <xref target="sec"/> to prevent fieldinjectioninjection, considerably more difficult and error-prone. Thus, this document opted for a flatter and more straightforward structure.</t> </section> <section anchor="the-whole-certificate-and-certificate-chain"> <name>The Whole Certificate and Certificate Chain</name> <t>Different applications will have varying requirements about what information from the client certificate is needed, such as the subject and/or issuer distinguished name, subject alternative name(s), serial number, subject public key info, fingerprint, etc. Furthermore, some applications, such as that described in <xref target="RFC8705"/>, make use of the entire certificate. In order to accommodate the latter and ensure wide applicability by not trying to cherry-pick particular certificate information, this document opted to pass the full, encoded certificate as the value of the<tt>Client-Cert</tt>Client-Cert field.</t> <t>The validation of the client certificate and chain of the mutually authenticated TLS connection is typically performed by the TTRP during the handshake. With the responsibility of certificate validation falling on the TTRP, the end-entity certificate is oftentimes sufficient for the needs of the origin server. The separate<tt>Client-Cert-Chain</tt>Client-Cert-Chain field can convey the certificate chain for origin server deployments that require this additional information.</t> </section> </section> <sectionanchor="acknowledgements">anchor="acknowledgements" toc="default" numbered="false"> <name>Acknowledgements</name> <t>The authors would like to thank the following individualswho'vewho have contributed to this document in variouswaysways, ranging from just being generally supportive of bringing forth the document to providing specific feedback or content:</t> <ul spacing="normal"><li>Evan Anderson</li> <li>Annabelle Backman</li> <li>Alan Frindell</li> <li>Rory Hewitt</li> <li>Fredrik Jeansson</li> <li>Benjamin Kaduk</li> <li>Torsten Lodderstedt</li> <li>Kathleen Moriarty</li> <li>Mark Nottingham</li> <li>Erik Nygren</li> <li>Mike Ounsworth</li> <li>Lucas Pardue</li> <li>Matt Peterson</li> <li>Eric Rescorla</li> <li>Justin Richer</li> <li>Michael Richardson</li> <li>Joe Salowey</li> <li>Rich Salz</li> <li>Mohit Sethi</li> <li>Rifaat Shekh-Yusef</li> <li>Travis Spencer</li> <li>Nick Sullivan</li> <li>Willy Tarreau</li> <li>Martin Thomson</li> <li>Peter Wu</li> <li>Hans Zandbelt</li> </ul> </section> <section anchor="document-history"> <name>Document History</name> <ul empty="true"> <li> <t>To be removed by the RFC Editor before publication as an RFC</t> </li> </ul> <t>draft-ietf-httpbis-client-cert-field-06</t> <ul spacing="normal"> <li>Updates from IESG review</li> </ul> <t>draft-ietf-httpbis-client-cert-field-05</t> <ul spacing="normal"> <li>Correct a couple references</li> <li>Updates from Genart Last Call review</li> <li>Incorporate AD review feedback</li> <li>Editorial updates</li> </ul> <t>draft-ietf-httpbis-client-cert-field-04</t> <ul spacing="normal"> <li>Updates, fixes, and clarifications from WGLC feedback</li> </ul> <t>draft-ietf-httpbis-client-cert-field-03</t> <ul spacing="normal"> <li>State that the certificate chain is in the same order as it appears in TLS rather than copying the language from TLS</li> <li>Update references for HTTP Semantics, HTTP/3, and QPACK to point to the now RFCs 9110/9114/9204</li> <li>HTTP Semantics now a normative ref</li> <li>Mention that origin server access control decisions can be conveyed by selecting response content or with a 403</li> </ul> <t>draft-ietf-httpbis-client-cert-field-02</t> <ul spacing="normal"> <li>Add a note about cert retention on TLS session resumption</li> <li>Say to use only the last one in the case of multiple post-handshake client cert authentications</li> </ul> <t>draft-ietf-httpbis-client-cert-field-01</t> <ul spacing="normal"> <li>Use RFC 8941 Structured Field Values for HTTP</li> <li>Introduce a separate header that can convey the certificate chain</li> <li>Add considerations on header compression and size</li> <li>Describe interaction with caching</li> <li>Fill out IANA Considerations with HTTP field name registrations</li> <li>Discuss renegotiation</li> </ul> <t>draft-ietf-httpbis-client-cert-field-00</t> <ul spacing="normal"> <li>Initial WG revision</li> <li>Mike Bishop added as co-editor</li> </ul> <t>draft-bdc-something-something-certificate-05</t> <ul spacing="normal"> <li>Change intended status of the draft to Informational</li> <li>Editorial updates and (hopefully) clarifications</li> </ul> <t>draft-bdc-something-something-certificate-04</t> <ul spacing="normal"> <li>Update reference from draft-ietf-oauth-mtls to RFC8705</li> </ul> <t>draft-bdc-something-something-certificate-03</t> <ul spacing="normal"> <li>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</li> </ul> <t>draft-bdc-something-something-certificate-02</t> <ul spacing="normal"> <li>Editorial tweaks + further discussion notes</li> </ul> <t>draft-bdc-something-something-certificate-01</t> <ul spacing="normal"> <li>Use the RFC v3 Format or die trying</li> </ul> <t>draft-bdc-something-something-certificate-00</t> <ul spacing="normal"> <li>Initial draft after a time constrained and rushed <eref target="https://datatracker.ietf.org/meeting/106/materials/slides-106-secdispatch-securing-protocols-between-proxies-and-backend-http-servers-00">secdispatch presentation</eref> at IETF 106 in Singapore with the recommendation to write up a draft (at the end of the <eref target="https://datatracker.ietf.org/meeting/106/materials/minutes-106-secdispatch">minutes</eref>) and some folks expressing interest despite the rather poor presentation</li><li><t><contact fullname="Evan Anderson"/></t></li> <li><t><contact fullname="Annabelle Backman"/></t></li> <li><t><contact fullname="Alan Frindell"/></t></li> <li><t><contact fullname="Rory Hewitt"/></t></li> <li><t><contact fullname="Fredrik Jeansson"/></t></li> <li><t><contact fullname="Benjamin Kaduk"/></t></li> <li><t><contact fullname="Torsten Lodderstedt"/></t></li> <li><t><contact fullname="Kathleen Moriarty"/></t></li> <li><t><contact fullname="Mark Nottingham"/></t></li> <li><t><contact fullname="Erik Nygren"/></t></li> <li><t><contact fullname="Mike Ounsworth"/></t></li> <li><t><contact fullname="Lucas Pardue"/></t></li> <li><t><contact fullname="Matt Peterson"/></t></li> <li><t><contact fullname="Eric Rescorla"/></t></li> <li><t><contact fullname="Justin Richer"/></t></li> <li><t><contact fullname="Michael Richardson"/></t></li> <li><t><contact fullname="Joe Salowey"/></t></li> <li><t><contact fullname="Rich Salz"/></t></li> <li><t><contact fullname="Mohit Sethi"/></t></li> <li><t><contact fullname="Rifaat Shekh-Yusef"/></t></li> <li><t><contact fullname="Travis Spencer"/></t></li> <li><t><contact fullname="Nick Sullivan"/></t></li> <li><t><contact fullname="Willy Tarreau"/></t></li> <li><t><contact fullname="Martin Thomson"/></t></li> <li><t><contact fullname="Peter Wu"/></t></li> <li><t><contact fullname="Hans Zandbelt"/></t></li> </ul> 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