--- 1/draft-ietf-httpbis-client-cert-field-00.txt 2022-01-25 16:13:11.396595497 -0800 +++ 2/draft-ietf-httpbis-client-cert-field-01.txt 2022-01-25 16:13:11.436596503 -0800 @@ -1,95 +1,100 @@ HTTP B. Campbell Internet-Draft Ping Identity Intended status: Informational M. Bishop, Ed. -Expires: 10 December 2021 Akamai - 8 June 2021 +Expires: 29 July 2022 Akamai + 25 January 2022 -Client-Cert HTTP Header Field: Conveying Client Certificate Information - from TLS Terminating Reverse Proxies to Origin Server Applications - draft-ietf-httpbis-client-cert-field-00 + Client-Cert HTTP Header Field + draft-ietf-httpbis-client-cert-field-01 Abstract - This document defines the HTTP header field "Client-Cert" that allows - a TLS terminating reverse proxy to convey the client certificate of a - mutually-authenticated TLS connection to the origin server in a - common and predictable manner. + This document defines HTTP extension header fields that allow a TLS + terminating reverse proxy to convey the client certificate + information of a mutually-authenticated TLS connection to the origin + server in a common and predictable manner. -Note to Readers +About This Document - _RFC EDITOR: please remove this section before publication_ + This note is to be removed before publishing as an RFC. - Discussion of this draft takes place on the HTTP working group - mailing list (ietf-http-wg@w3.org), which is archived at - https://lists.w3.org/Archives/Public/ietf-http-wg/ - (https://lists.w3.org/Archives/Public/ietf-http-wg/). + Status information for this document may be found at + https://datatracker.ietf.org/doc/draft-ietf-httpbis-client-cert- + field/. - Working Group information can be found at http://httpwg.github.io/ - (http://httpwg.github.io/); source code and issues list for this - draft can be found at https://github.com/httpwg/http- - extensions/labels/client-cert-header (https://github.com/httpwg/http- - extensions/labels/client-cert-header). + Discussion of this document takes place on the HTTP Working Group + mailing list (mailto:ietf-http-wg@w3.org), which is archived at + https://lists.w3.org/Archives/Public/ietf-http-wg/. Working Group + information can be found at https://httpwg.org/. + + Source for this draft and an issue tracker can be found at + https://github.com/httpwg/http-extensions/labels/client-cert-field. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on 10 December 2021. + This Internet-Draft will expire on 29 July 2022. Copyright Notice - Copyright (c) 2021 IETF Trust and the persons identified as the + Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components - extracted from this document must include Simplified BSD License text - as described in Section 4.e of the Trust Legal Provisions and are - provided without warranty as described in the Simplified BSD License. + extracted from this document must include Revised BSD License text as + described in Section 4.e of the Trust Legal Provisions and are + provided without warranty as described in the Revised BSD License. Table of Contents - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Notation and Conventions . . . . . . . . . . 4 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 - 2. HTTP Header Field and Processing Rules . . . . . . . . . . . 4 - 2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 4 + 2. HTTP Header Fields and Processing Rules . . . . . . . . . . . 4 + 2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Client-Cert HTTP Header Field . . . . . . . . . . . . . . 5 - 2.3. Processing Rules . . . . . . . . . . . . . . . . . . . . 5 - 3. Security Considerations . . . . . . . . . . . . . . . . . . . 6 - 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 - 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 5.1. Normative References . . . . . . . . . . . . . . . . . . 7 - 5.2. Informative References . . . . . . . . . . . . . . . . . 7 - Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 9 - Appendix B. Considerations Considered . . . . . . . . . . . . . 10 - B.1. Header Injection . . . . . . . . . . . . . . . . . . . . 10 - B.2. The Forwarded HTTP Extension . . . . . . . . . . . . . . 10 - B.3. The Whole Certificate and Only the Whole Certificate . . 11 - Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 12 - Appendix D. Document History . . . . . . . . . . . . . . . . . . 13 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 + 2.3. Client-Cert-Chain HTTP Header Field . . . . . . . . . . . 6 + 2.4. Processing Rules . . . . . . . . . . . . . . . . . . . . 6 + 3. Deployment Considerations . . . . . . . . . . . . . . . . . . 7 + 3.1. Header Field Compression . . . . . . . . . . . . . . . . 8 + 3.2. Header Block Size . . . . . . . . . . . . . . . . . . . . 8 + 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 + 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 + 5.1. HTTP Field Name Registrations . . . . . . . . . . . . . . 9 + 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 + 6.1. Normative References . . . . . . . . . . . . . . . . . . 10 + 6.2. Informative References . . . . . . . . . . . . . . . . . 10 + Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 12 + Appendix B. Considerations Considered . . . . . . . . . . . . . 13 + B.1. Field Injection . . . . . . . . . . . . . . . . . . . . . 14 + B.2. The Forwarded HTTP Extension . . . . . . . . . . . . . . 14 + B.3. The Whole Certificate and Certificate Chain . . . . . . . 14 + Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 15 + Appendix D. Document History . . . . . . . . . . . . . . . . . . 16 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 1. Introduction 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 the internet 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 @@ -107,285 +112,421 @@ authentication is sometimes employed 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, and the respective validation of such bindings. The specific details from the certificate needed also 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. A common way this information is conveyed in practice today - is by using non-standard headers to carry the certificate (in some + is by using non-standard fields to carry the certificate (in some encoding) or individual parts thereof in the HTTP request that is dispatched to the origin server. This solution works but interoperability between independently developed components can be cumbersome or even impossible depending on the implementation choices - respectively made (like what header names are used or are + respectively made (like what field names are used or are configurable, which parts of the certificate are exposed, or how the certificate is encoded). A well-known predictable approach to this commonly occurring functionality could improve and simplify interoperability between independent implementations. - This document aspires to standardize an HTTP header field named - "Client-Cert" that a TLS terminating reverse proxy (TTRP) adds to - requests that it sends to the backend origin servers. The header - value contains the client certificate from the mutually-authenticated - TLS connection between the originating client and the TTRP. 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 "Client-Cert" header is intentionally limited to - exposing to the origin server the certificate that was presented by - the originating client in its connection to the TTRP. + This document aspires to standardize two HTTP header fields, Client- + Cert and Client-Cert-Chain, which a TLS terminating reverse proxy + (TTRP) adds to requests sent to the backend origin servers. The + 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 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 Client-Cert header field + is intentionally limited to exposing to the origin server the + certificate that was presented by the originating client in its + connection to the TTRP. 1.1. Requirements Notation and Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and - "OPTIONAL" in this document are to be interpreted as described in BCP - 14 [RFC2119] [RFC8174] when, and only when, they appear in all + "OPTIONAL" in this document are to be interpreted as described in + BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 1.2. Terminology Phrases like TLS client certificate authentication or mutually- authenticated TLS 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 [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 [RFC8446] [RFC5246] this requires that the client send the Certificate and CertificateVerify messages during the handshake and for the server to verify the CertificateVerify and Finished messages. - TODO: HTTP2 forbids TLS renegotiation and post-handshake - authentication but it's possible with HTTP1.1 and maybe needs to - be discussed explicitly here or somewhere in this document? - Naively I'd say that the "Client-Cert" header will be sent with - the data of the most recent client cert anytime after - renegotiation or post-handshake auth. And only for requests that - are fully covered by the cert but that in practice making the - determination of where exactly in the application data the cert - messages arrived is hard to impossible so it'll be a best effort - kind of thing. + HTTP/2 restricts TLS 1.2 renegotiation (Section 9.2.1 of [RFC7540]) + and prohibits TLS 1.3 post-handshake authentication [RFC8740]. + However, they are sometimes used to implement reactive client + certificate authentication in HTTP/1.1 [RFC7230] 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. -2. HTTP Header Field and Processing Rules +2. HTTP Header Fields and Processing Rules -2.1. Encoding + This document designates the following headers, defined further in + Section 2.2 and Section 2.3 respectively, to carry the client + certificate information of a mutually-authenticated TLS connection + from a reverse proxy to origin server. - The field-values of the HTTP header defined herein utilize the - following encoded form. + Client-Cert: Conveys the end-entity certificate used by the client + in the TLS handshake with the reverse proxy from the reverse proxy + to the origin server. - A certificate is represented in text as an "EncodedCertificate", - which is the base64-encoded (Section 4 of [RFC4648]) DER - [ITU.X690.1994] PKIX certificate. The encoded value MUST NOT include - any line breaks, whitespace, or other additional characters. ABNF - [RFC5234] syntax for "EncodedCertificate" is shown in the figure - below. + Client-Cert-Chain: Conveys the certificate chain used for validation + of the end-entity certificate used by the client in the TLS + handshake from the reverse proxy to the origin server. - EncodedCertificate = 1*( DIGIT / ALPHA / "+" / "/" ) 0*2"=" +2.1. Encoding - DIGIT = ; A-Z / a-z - ALPHA = ; 0-9 + The headers in this document encode certificates as Structured Field + Byte Sequences (Section 3.3.5 of [RFC8941]) where the value of the + binary data is a DER encoded [ITU.X690.1994] X.509 certificate + [RFC5280]. In effect, this means that the binary DER certificate is + encoded using base64 (without line breaks, spaces, or other + characters outside the base64 alphabet) and delimited with colons on + either side. + + Note that certificates are often stored encoded in a textual format, + such as the one described in Section 5.1 of [RFC7468], which is + already nearly compatible with a Structured Field Byte Sequence; if + so, it will be sufficient to replace ---(BEGIN|END) CERTIFICATE--- + with : and remove line breaks in order to generate an appropriate + item. 2.2. Client-Cert HTTP Header Field - In the context of a TLS terminating reverse proxy (TTRP) deployment, - the TTRP makes the TLS client certificate available to the backend - application with the following header field. + 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. - Client-Cert: The end-entity client certificate as an - "EncodedCertificate" value. + Client-Cert is an Item Structured Header [RFC8941]. Its value MUST + be a Byte Sequence (Section 3.3.5 of [RFC8941]). Its ABNF is: - The "Client-Cert" header field defined herein is only for use in HTTP - requests and MUST NOT be used in HTTP responses. It is a single HTTP - header field-value as defined in Section 3.2 of [RFC7230], which MUST - NOT have a list of values or occur multiple times in a request. + Client-Cert = sf-binary -2.3. Processing Rules + The value of the header is encoded as described in Section 2.1. + + The Client-Cert header field is only for use in HTTP requests and + MUST NOT be used in HTTP responses. It is a single HTTP header field + value as defined in Section 3.2 of [RFC7230], which MUST NOT have a + list of values or occur multiple times in a request. + +2.3. Client-Cert-Chain HTTP Header Field + + In the context of a TLS terminating reverse proxy deployment, the + proxy MAY make the certificate chain used for validation of the end- + entity certificate available to the backend application with the + Client-Cert-Chain HTTP header field. This field contains + certificates used by the proxy to validate the certificate used by + the client in the TLS handshake. These certificates might or might + not have been provided by the client during the TLS handshake. + + Client-Cert-Chain is a List Structured Header [RFC8941]. Each item + in the list MUST be a Byte Sequence (Section 3.3.5 of [RFC8941]) + encoded as described in Section 2.1. + + The header's ABNF is: + + Client-Cert-Chain = sf-list + + The Client-Cert-Chain header field is only for use in HTTP requests + and MUST NOT be used in HTTP responses. It MAY have a list of values + or occur multiple times in a request. For header compression + purposes, it might be advantageous to split lists into multiple + instances. + + The first certificate in the list SHOULD directly certify the end- + entity certificate provided in the Client-Cert header; each following + certificate SHOULD directly certify the one immediately preceding it. + Because certificate validation requires that trust anchors be + distributed independently, a certificate that specifies a trust + anchor MAY be omitted from the chain, provided that the server is + known to possess any omitted certificates. + + However, for maximum compatibility, servers SHOULD be prepared to + handle potentially extraneous certificates and arbitrary orderings. + +2.4. Processing Rules This section outlines the applicable processing rules for a TLS terminating reverse proxy (TTRP) that has negotiated a mutually- authenticated TLS connection to convey the client certificate from that connection to the backend origin servers. Use of the technique is to be a configuration or deployment option and the processing rules described herein are for servers operating with that option enabled. A TTRP negotiates the use of a mutually-authenticated TLS connection with the client, such as is described in [RFC8446] or [RFC5246], and validates the client certificate per its policy and trusted certificate authorities. Each HTTP request on the underlying TLS connection are dispatched to the origin server with the following modifications: - 1. The client certificate is be placed in the "Client-Cert" header - field of the dispatched request as defined in Section 2.2. + 1. The client certificate is placed in the Client-Cert header field + of the dispatched request, as described in Section 2.2. - 2. Any occurrence of the "Client-Cert" header in the original - incoming request MUST be removed or overwritten before forwarding - the request. An incoming request that has a "Client-Cert" header - MAY be rejected with an HTTP 400 response. + 2. If so configured, the validation chain of the client certificate + is placed in the Client-Cert-Chain header field of the request, + as described in Section 2.3. + + 3. Any occurrence of the Client-Cert or Client-Cert-Chain header + fields in the original incoming request MUST be removed or + overwritten before forwarding the request. An incoming request + that has a Client-Cert or Client-Cert-Chain header field MAY be + rejected with an HTTP 400 response. Requests made over a TLS connection where the use of client certificate authentication was not negotiated MUST be sanitized by - removing any and all occurrences "Client-Cert" header field prior to - dispatching the request to the backend server. + removing any and all occurrences of the Client-Cert and Client-Cert- + Chain header fields prior to dispatching the request to the backend + server. - Backend origin servers may then use the "Client-Cert" header of the - request to determine if the connection from the client to the TTRP - was mutually-authenticated and, if so, the certificate thereby + Backend origin servers may then use the 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. - Forward proxies and other intermediaries MUST NOT add the "Client- - Cert" header to requests, or modify an existing "Client-Cert" header. - Similarly, clients MUST NOT employ the "Client-Cert" header in + Forward proxies and other intermediaries MUST NOT add the Client-Cert + or Client-Cert-Chain header fields to requests, or modify an existing + Client-Cert or Client-Cert-Chain header field. Similarly, clients + MUST NOT employ the Client-Cert or Client-Cert-Chain header field in requests. - A server that receives a request with a "Client-Cert" header value - that it considers to be too large can respond with an HTTP 431 status - code per Section 5 of [RFC6585]. + When the value of the Client-Cert request header field is used to + select a response (e.g., the response content is access-controlled), + the response MUST either be uncacheable (e.g., by sending Cache- + Control: no-store) or be designated for selective reuse only for + subsequent requests with the same Client-Cert header value by sending + a Vary: Client-Cert response header. If a TTRP encounters a response + with a client-cert field name in the Vary header field, it SHOULD + prevent the user agent from caching the response by transforming the + value of the Vary response header field to *. -3. Security Considerations +3. Deployment Considerations +3.1. Header Field Compression - The header described herein enable a TTRP and backend or origin - server to function together as though, from the client's perspective, - they are a single logical server side deployment of HTTPS over a - mutually-authenticated TLS connection. Use of the "Client-Cert" - header outside that intended use case, however, may undermine the - protections afforded by TLS client certificate authentication. - Therefore steps MUST be taken to prevent unintended use, both in - sending the header and in relying on its value. + If the client certificate header field is generated by an + intermediary on a connection that compresses fields (e.g., using + HPACK [RFC7541] or QPACK [I-D.ietf-quic-qpack]) and more than one + client's requests are multiplexed into that connection, it can reduce + compression efficiency significantly, due to the typical size of the + field value and its variation between clients. Recipients that + anticipate connections with these characteristics can mitigate the + efficiency loss by increasing the size of the dynamic table. If a + recipient does not do so, senders may find it beneficial to always + send the field value as a literal, rather than entering it into the + dynamic table. - Producing and consuming the "Client-Cert" header SHOULD be a - configurable option, respectively, in a TTRP and backend server (or - individual application in that server). The default configuration - for both should be to not use the "Client-Cert" header thus requiring - an "opt-in" to the functionality. +3.2. Header Block Size - In order to prevent header injection, backend servers MUST only - accept the "Client-Cert" header from a trusted TTRP (or other proxy - in a trusted path from the TTRP). A TTRP MUST sanitize the incoming - request before forwarding it on by removing or overwriting any - existing instances of the header. Otherwise arbitrary clients can - control the header value as seen and used by the backend server. It - is important to note that neglecting to prevent header 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 header sanitation is in - place. + A server in receipt of a larger header block than it is willing to + 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 + field values containing certificate data, recipients may need to be + configured to allow for a larger maximum header block size. An + intermediary generating client certificate header fields on + connections that allow for advertising the maximum acceptable header + block size (e.g. HTTP/2 [RFC7540] or HTTP/3 [I-D.ietf-quic-http]) + should account for the additional size of header block of the + requests it sends vs. requests it receives by advertising a value to + its clients that is sufficiently smaller so as to allow for the + addition of certificate data. + +4. Security Considerations + + The header fields described herein enable a TTRP and backend or + origin server to function together as though, from the client's + perspective, they are a single logical server side deployment of + HTTPS over a mutually-authenticated TLS connection. Use of the + header fields outside that intended use case, however, may undermine + the protections afforded by TLS client certificate authentication. + Therefore, steps MUST be taken to prevent unintended use, both in + sending the header field and in relying on its value. + + Producing and consuming the Client-Cert and Client-Cert-Chain header + fields SHOULD be configurable options, respectively, in a TTRP and + backend server (or individual application in that server). The + default configuration for both should be to not use the header fields + thus requiring an "opt-in" to the functionality. + + In order to prevent field injection, backend servers MUST only accept + the Client-Cert and Client-Cert-Chain header fields from a trusted + TTRP (or other proxy in a trusted path from the TTRP). A TTRP MUST + sanitize the incoming request before forwarding it on by removing or + overwriting any existing instances of the fields. Otherwise, + arbitrary clients can control the field values as seen and used by + the backend server. It is important to note that neglecting to + prevent field injection does not "fail safe" in that the nominal + functionality will still work as expected even when malicious actions + are possible. As such, extra care is recommended in ensuring that + proper field sanitation is in place. The communication between a TTRP and backend server needs to be secured against eavesdropping and modification by unintended parties. The configuration options and request sanitization are necessarily functionally of the respective servers. The other requirements can be met in a number of ways, which will vary based on specific deployments. The communication between a TTRP and backend or origin server, for example, might be authenticated in some way with the - insertion and consumption of the "Client-Cert" header occurring only - on that connection. Alternatively the network topology might dictate - a private network such that the backend application is only able to - accept requests from the TTRP and the proxy can only make requests to - that server. Other deployments that meet the requirements set forth - herein are also possible. + insertion and consumption of the Client-Cert and Client-Cert-Chain + header fields occurring only on that connection. Alternatively the + network topology might dictate a private network such that the + backend application is only able to accept requests from the TTRP and + the proxy can only make requests to that server. Other deployments + that meet the requirements set forth herein are also possible. -4. IANA Considerations +5. IANA Considerations - TODO: register the "Client-Cert" HTTP header field in the registry - defined by http-core. +5.1. HTTP Field Name Registrations -5. References + Please register the following entries in the "Hypertext Transfer + Protocol (HTTP) Field Name Registry" defined by + [I-D.ietf-httpbis-semantics]: -5.1. Normative References + * Field name: Client-Cert + + * Status: permanent + + * Specification document: Section 2 of [this document] + + * Field name: Client-Cert-Chain + + * Status: permanent + + * Specification document: Section 2 of [this document] + +6. References +6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, . - [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data - Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, - . - [ITU.X690.1994] International Telecommunications Union, "Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITU-T Recommendation X.690, 1994. -5.2. Informative References + [RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for + HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, + . + +6.2. Informative References [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, . - [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax - Specifications: ABNF", STD 68, RFC 5234, - DOI 10.17487/RFC5234, January 2008, - . + [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext + Transfer Protocol Version 2 (HTTP/2)", RFC 7540, + DOI 10.17487/RFC7540, May 2015, + . + + [RFC8740] Benjamin, D., "Using TLS 1.3 with HTTP/2", RFC 8740, + DOI 10.17487/RFC8740, February 2020, + . [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014, . + [RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX, + PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468, + April 2015, . + + [RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for + HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, + . + + [I-D.ietf-quic-qpack] + Krasic, C. '., Bishop, M., and A. Frindell, "QPACK: Header + Compression for HTTP/3", Work in Progress, Internet-Draft, + draft-ietf-quic-qpack-21, 2 February 2021, + . + [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012, . + [I-D.ietf-quic-http] + Bishop, M., "Hypertext Transfer Protocol Version 3 + (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf- + quic-http-34, 2 February 2021, + . + + [I-D.ietf-httpbis-semantics] + Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP + Semantics", Work in Progress, Internet-Draft, draft-ietf- + httpbis-semantics-19, 12 September 2021, + . + [RFC7239] Petersson, A. and M. Nilsson, "Forwarded HTTP Extension", RFC 7239, DOI 10.17487/RFC7239, June 2014, . [RFC8705] Campbell, B., Bradley, J., Sakimura, N., and T. Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens", RFC 8705, DOI 10.17487/RFC8705, February 2020, . - [RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for - HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, - . - - [RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J., - Weiler, S., and T. Kivinen, "Using Raw Public Keys in - Transport Layer Security (TLS) and Datagram Transport - Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, - June 2014, . - Appendix A. Example In a hypothetical example where a TLS client presents the client and intermediate certificate from Figure 1 when establishing a mutually- authenticated TLS connection with the TTRP, the proxy would send the - "Client-Cert" header shown in {#example-header} to the backend. Note - that line breaks and whitespace have been added to the value of the - header field in Figure 2 for display and formatting purposes only. + Client-Cert field shown in {#example-header} to the backend. Note + that line breaks and whitespace have been added to the field value in + Figure 2 for display and formatting purposes only. -----BEGIN CERTIFICATE----- MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJMZXQncyBB dXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0yMDAx MTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZI zj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p 5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIw ADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMC BsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1w bGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMje @@ -413,190 +554,203 @@ cml0eTBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABFoaHU+Z5bPKmGzlYXtCf+E6 HYj62fORaHDOrt+yyh3H/rTcs7ynFfGn+gyFsrSP3Ez88rajv+U2NfD0o0uZ4Pmj YzBhMB0GA1UdDgQWBBTEA2Q6eecKu9g9yb5glbkhhVINGDAfBgNVHSMEGDAWgBTE A2Q6eecKu9g9yb5glbkhhVINGDAPBgNVHRMBAf8EBTADAQH/MA4GA1UdDwEB/wQE AwIBhjAKBggqhkjOPQQDAgNIADBFAiEAmAeg1ycKHriqHnaD4M/UDBpQRpkmdcRF YGMg1Qyrkx4CIB4ivz3wQcQkGhcsUZ1SOImd/lq1Q0FLf09rGfLQPWDc -----END CERTIFICATE----- Figure 1: Certificate Chain (with client certificate first) - Client-Cert: MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJM - ZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0y - MDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZI - zj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p5Be5 - F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIwADAfBgNV - HSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMCBsAwEwYDVR0l - BAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1wbGUuY29tMAoGCCqG - SM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMjeSkC3dFCOOB8TAiEAx/kH - SB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk= + Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKDBJ + MZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQTAeFw0 + yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFkwEwYHKoZ + Izj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmckC8vdgJ1p5Be + 5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDVR0TBAIwADAfBgN + VHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf8EBAMCBsAwEwYDVR0 + lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV4YW1wbGUuY29tMAoGCCq + GSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6bMjeSkC3dFCOOB8TAiEAx/k + HSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=: - Figure 2: Header in HTTP Request to Origin Server + Figure 2: Header Field in HTTP Request to Origin Server -Appendix B. Considerations Considered + If the proxy were configured to also include the certificate chain, + it would also include this header: -B.1. Header Injection + Client-Cert-Chain: :MIIB5jCCAYugAwIBAgIBFjAKBggqhkjOPQQDAjBWMQsw + 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: - This draft requires that the TTRP sanitize the headers of the - incoming request by removing or overwriting any existing instances of - the "Client-Cert" header before dispatching that request to the - backend application. Otherwise, a client could inject its own - "Client-Cert" header that would appear to the backend to have come + Figure 3: Certificate Chain in HTTP Request to Origin Server + +Appendix B. Considerations Considered +B.1. Field Injection + + This draft requires that the TTRP sanitize the fields of the incoming + request by removing or overwriting any existing instances of the + Client-Cert and Client-Cert-Chain header fields before dispatching + that request to the backend application. Otherwise, a client could + inject its own values that would appear to the backend to have come from the TTRP. Although numerous other methods of detecting/ - preventing header injection are possible; such as the use of a unique - secret value as part of the header name or value or the application - of a signature, HMAC, or AEAD, there is no common general - standardized mechanism. The potential problem of client header - injection is not at all unique to the functionality of this draft and - it would therefor be inappropriate for this draft to define a one-off - solution. In the absence of a generic standardized solution existing - currently, stripping/sanitizing the headers is the de facto means of - protecting against header injection in practice today. Sanitizing - the headers is sufficient when properly implemented and is normative - requirement of Section 3. + 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 standardized + mechanism. The potential problem of client field injection is not at + all unique to the functionality of this draft, and it would therefore + be inappropriate for this draft to define a one-off solution. In the + absence of a generic standardized solution existing currently, + stripping/sanitizing the fields is the de facto means of protecting + against field injection in practice today. Sanitizing the fields is + sufficient when properly implemented and is a normative requirement + of Section 4. 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 TLS client certificate information of concern to this draft could - have been communicated with an extension parameter to the "Forwarded" - header field, however, doing so would have had some disadvantages - that this draft endeavored to avoid. The "Forwarded" header syntax - allows for information about a full chain of proxied HTTP requests, - whereas the "Client-Cert" header of this document is 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 "Forwarded" header is + have been communicated with an extension parameter to the Forwarded + field; however, doing so would have had some disadvantages that this + draft endeavored to avoid. The Forwarded field syntax allows for + information about a full chain of proxied HTTP requests, whereas the + Client-Cert and 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 Forwarded field is expressive but also more complicated, which would make processing it more cumbersome, and more importantly, make properly sanitizing its - content as required by Section 3 to prevent header injection - considerably more difficult and error prone. Thus, this draft opted - for the flatter and more straightforward structure of a single - "Client-Cert" header. + content as required by Section 4 to prevent field injection + considerably more difficult and error-prone. Thus, this draft opted + for a flatter and more straightforward structure. -B.3. The Whole Certificate and Only the Whole Certificate +B.3. The Whole Certificate and Certificate Chain Different applications will have varying requirements about what 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 "OAuth 2.0 Mutual-TLS Client - Authentication and Certificate-Bound Access Tokens" [RFC8705], make - use of the entire certificate. In order to accommodate the latter - and ensure wide applicability by not trying to cherry-pick particular + Furthermore, some applications, such as [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 draft opted to pass the full encoded - certificate as the value of the "Client-Cert" header. + certificate as the value of the Client-Cert field. The handshake and validation of the client certificate (chain) of the mutually-authenticated TLS connection is performed by the TTRP. With - the responsibility of certificate validation falling on the TTRP, - only the end-entity certificate is passed to the backend - the root - Certificate Authority is not included nor are any intermediates. - - TODO: It has been suggested that more information about the - certificate chain might be needed/wanted by the backend - application (to independently evaluate the cert chain, for - example, although that seems like it would be terribly - inefficient) and that any intermediates as well as the root should - also be somehow conveyed, which is an area for further discussion - should this draft progress. One potential approach suggested by a - few folks is to allow some configurability in what is sent along - with maybe a prefix token to indicate what's being sent - - something like "Client-Cert: FULL \ \ - \" or "Client-Cert: EE \" as the strawman. Or a - perhaps a parameter or other construct of [RFC8941] to indicate - what's being sent. It's also been suggested that the end-entity - certificate by itself might sometimes be too big (esp. e.g., with - some post-quantum signature schemes). Hard to account for it both - being too much data and not enough data at the same time. But - potentially opening up configuration options to send only specific - attribute(s) from the client certificate is a possibility for - that. In the author's humble opinion the end-entity certificate - by itself strikes a good balance for the vast majority of needs - and avoids optionality. But, again, this is an area for further - discussion should this draft progress. - - TODO: It has also been suggested that maybe considerations for - [RFC7250] Raw Public Keys is maybe worth considering. This too is - this is an area for further discussion and consideration should - this draft progress. + 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 Client-Cert-Chain field can convey the + certificate chain for deployments that require such information. Appendix C. Acknowledgements - The author would like to thank the following individuals who've + The authors would like to thank the following individuals who've contributed in various ways ranging from just being generally supportive of bringing forth the draft to providing specific feedback or content: * Evan Anderson * Annabelle Backman - * Mike Bishop + * Alan Frindell * Rory Hewitt * Fredrik Jeansson * Benjamin Kaduk * Torsten Lodderstedt * Kathleen Moriarty * Mark Nottingham + * Erik Nygren + * Mike Ounsworth * Matt Peterson * Eric Rescorla * Justin Richer * Michael Richardson - * Joe Salowey * Rich Salz * Mohit Sethi * Rifaat Shekh-Yusef + * Travis Spencer * Nick Sullivan + * Martin Thomson + * Peter Wu * Hans Zandbelt Appendix D. Document History To be removed by the RFC Editor before publication as an RFC + draft-ietf-httpbis-client-cert-field-01 + + * Use RFC 8941 Structured Field Values for HTTP + + * Introduce a separate header that can convey the certificate chain + + * Add considerations on header compression and size + + * Describe interaction with caching + + * Fill out IANA Considerations with HTTP field name registrations + + * Discuss renegotiation + draft-ietf-httpbis-client-cert-field-00 * Initial WG revision * Mike Bishop added as co-editor draft-bdc-something-something-certificate-05 * Change intended status of the draft to Informational * Editorial updates and (hopefully) clarifications - - draft-bdc-something-something-certificate-04 - * Update reference from draft-ietf-oauth-mtls to RFC8705 draft-bdc-something-something-certificate-03 * 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