HTTP Proxy-Status Parameter for Next-Hop Aliases
draft-ietf-httpbis-alias-proxy-status-00

HTTP                                                            T. Pauly
Internet-Draft                                               Apple, Inc.
Intended status: Standards Track                          4 January 2023
Expires: 8 July 2023

            HTTP Proxy-Status Parameter for Next-Hop Aliases
                draft-ietf-httpbis-alias-proxy-status-00

Abstract

   This document defines an HTTP Proxy-Status Parameter that contains a
   list of aliases received over DNS when establishing a connection to
   the next hop.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-httpbis-alias-proxy-
   status/.

   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/alias-proxy-status.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 8 July 2023.

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Copyright Notice

   Copyright (c) 2023 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
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   3
   2.  next-hop-aliases Parameter  . . . . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Proxy-Status HTTP response field [PROXY-STATUS] allows proxies to
   convey information about how a proxied request was handled in HTTP
   responses sent to clients.  It defines a set of parameters that
   provide information, such as the name of the next hop.

   [PROXY-STATUS] defines a next-hop parameter, which can contain a
   hostname, IP address, or alias of the next hop.  This parameter can
   contain only one such item, so it cannot be used to communicate a
   chain of aliases encountered during DNS resolution when connecting to
   the next hop.

   Knowing the full chain of aliases that were used during DNS
   resolution is particularly useful for clients of forward proxies, in
   which the client is requesting to connect to a specific target
   hostname using the CONNECT method [HTTP] or UDP proxying
   [CONNECT-UDP].  DNS aliases can be used to "cloak" hosts that perform
   tracking or malicious activity behind more innocuous hostnames, and
   clients such as web browsers use the chain of DNS aliases to
   influence behavior like cookie usage policies [COOKIES] or blocking
   of malicious hosts.

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   This document allows clients to receive the chain of DNS aliases for
   the next hop by including the list of names in a new next-hop-aliases
   Proxy-Status parameter.

1.1.  Requirements

   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.

2.  next-hop-aliases Parameter

   The next-hop-aliases parameter's value is a String that contains one
   or more DNS names in a comma-separated list.  The items in the list
   include all names received in CNAME records [DNS] during the course
   of resolving the next hop's hostname using DNS.  Since DNS names can
   include comma (,) characters in them, any commas that appear in a DNS
   names MUST be represented using a percent-encoded %2C value instead.
   The aliases SHOULD appear in the order in which they were received in
   DNS; that is, if a name has a CNAME record with a first alias, which
   has a CNAME record for a second alias, the aliases should appear in
   that order.

   For example:

   Proxy-Status: proxy.example.net; next-hop=2001:db8::1;
       next-hop-aliases="tracker.example.com.,service1.example-cdn.com."

   indicates that proxy.example.net, which used the IP address
   "2001:db8::1" as the next hop for this request, encountered the
   CNAMEs "tracker.example.com." and "service1.example-cdn.com" in the
   DNS resolution chain.  Note that while this example includes both the
   next-hop and next-hop-aliases parameters, next-hop-aliases can be
   included without including next-hop.

   The next-hop-aliases parameter only applies when DNS was used to
   resolve the next hop's name, and does not apply in all situations.
   Clients can use the information in this parameter to determine how to
   use the connection established through the proxy, but need to
   gracefully handle situations in which this parameter is not present.

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3.  Security Considerations

   The next-hop-aliases parameter does not include any DNSSEC
   information or imply that DNSSEC was used.  The information included
   in the parameter can only be trusted to be valid insofar as the
   client trusts its proxy to provide accurate information.  This
   information is intended to be used as a hint, and SHOULD NOT be used
   for making security decisions about the identity of a resource
   accessed through the proxy.

4.  IANA Considerations

   This document registers the "next-hop-aliases" parameter in the "HTTP
   Proxy-Status Parameters" registry <https://www.iana.org/assignments/
   http-proxy-status>.

   Name:  next-hop-aliases

   Description:  A string containing one or more DNS alises used to
      establish a proxied connection to the next hop.

   Reference:  This document

5.  References

5.1.  Normative References

   [CONNECT-UDP]
              Schinazi, D., "Proxying UDP in HTTP", RFC 9298,
              DOI 10.17487/RFC9298, August 2022,
              <https://www.rfc-editor.org/rfc/rfc9298>.

   [DNS]      Barr, D., "Common DNS Operational and Configuration
              Errors", RFC 1912, DOI 10.17487/RFC1912, February 1996,
              <https://www.rfc-editor.org/rfc/rfc1912>.

   [HTTP]     Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

   [PROXY-STATUS]
              Nottingham, M. and P. Sikora, "The Proxy-Status HTTP
              Response Header Field", RFC 9209, DOI 10.17487/RFC9209,
              June 2022, <https://www.rfc-editor.org/rfc/rfc9209>.

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   [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/rfc/rfc2119>.

   [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/rfc/rfc8174>.

5.2.  Informative References

   [COOKIES]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              DOI 10.17487/RFC6265, April 2011,
              <https://www.rfc-editor.org/rfc/rfc6265>.

Author's Address

   Tommy Pauly
   Apple, Inc.
   Email: tpauly@apple.com

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