HTTP Working GroupM. Nottingham
Internet-DraftFastly
Intended status: Standards TrackP. Sikora
Expires: September 2, 2020Google
March 1, 2020

The Proxy-Status HTTP Response Header Field

Abstract

This document defines the Proxy-Status HTTP header field to convey the details of intermediary handling of responses, including generated errors.

Note to Readers

RFC EDITOR: please remove this section before publication

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/.

Working Group information can be found at https://httpwg.org/; source code and issues list for this draft can be found at https://github.com/httpwg/http-extensions/labels/proxy-status.

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 http://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 September 2, 2020.

Copyright Notice

Copyright (c) 2020 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.



1. Introduction

HTTP intermediaries – including both forward proxies and gateways (also known as “reverse proxies”) – have become an increasingly significant part of HTTP deployments. In particular, reverse proxies and Content Delivery Networks (CDNs) form part of the critical infrastructure of many Web sites.

Typically, HTTP intermediaries forward requests towards the origin server and then forward their responses back to clients. However, if an error occurs, the response is generated by the intermediary itself.

HTTP accommodates these types of errors with a few status codes; for example, 502 Bad Gateway and 504 Gateway Timeout. However, experience has shown that more information is necessary to aid debugging and communicate what’s happened to the client.

Additionally, intermediaries sometimes want to convey additional information about their handling of a response, even if they did not generate it.

To enable these uses, Section 2 defines a new HTTP response header field to allow intermediaries to convey details of their handling of a response, and Section 2.2 defines a set of Proxy Error Types for use when a proxy generates the response. Section 2.3 explains how to define new Proxy Error Types.

1.1. Notational Conventions

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

This specification uses Structured Headers [I-D.ietf-httpbis-header-structure] to specify syntax. The terms sh-param-list, sh-item, sh-string, sh-token and sh-integer refer to the structured types defined therein.

Note that in this specification, “proxy” is used to indicate both forward and reverse proxies, otherwise known as gateways. “Next hop” indicates the connection in the direction leading to the origin server for the request.



3. IANA Considerations

Upon publication, please create the HTTP Proxy Error Types registry at https://iana.org/assignments/http-proxy-statuses and populate it with the types defined in Section 2.2; see Section 2.3 for its associated procedures.


4. Security Considerations

One of the primary security concerns when using Proxy-Status is leaking information that might aid an attacker. For example, information about the intermediary’s configuration and back-end topology can be exposed.

As a result, care needs to be taken when deciding to generate a Proxy-Status header. Note that intermediaries are not required to generate a Proxy-Status header field in any response, and can conditionally generate them based upon request attributes (e.g., authentication tokens, IP address).

Likewise, generation of all parameters is optional.


5. References

5.1. Normative References

[I-D.ietf-httpbis-header-structure]
Nottingham, M. and P. Kamp, “Structured Headers for HTTP”, Internet-Draft draft-ietf-httpbis-header-structure-15 (work in progress), January 2020.
[RFC2119]
Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels”, BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.
[RFC7301]
Friedl, S., Popov, A., Langley, A., and E. Stephan, “Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension”, RFC 7301, DOI 10.17487/RFC7301, July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[RFC8126]
Cotton, M., Leiba, B., and T. Narten, “Guidelines for Writing an IANA Considerations Section in RFCs”, BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174]
Leiba, B., “Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words”, BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8499]
Hoffman, P., Sullivan, A., and K. Fujiwara, “DNS Terminology”, BCP 219, RFC 8499, DOI 10.17487/RFC8499, January 2019, <https://www.rfc-editor.org/info/rfc8499>.

5.2. Informative References

[RFC8586]
Ludin, S., Nottingham, M., and N. Sullivan, “Loop Detection in Content Delivery Networks (CDNs)”, RFC 8586, DOI 10.17487/RFC8586, April 2019, <https://www.rfc-editor.org/info/rfc8586>.

Authors' Addresses

Mark Nottingham
Fastly
EMail: mnot@mnot.net
URI: https://www.mnot.net/
Piotr Sikora
Google
EMail: piotrsikora@google.com