HTTP Working Group T. Pauly Internet-Draft Apple, Inc. Intended status: Standards Track January 4, 2023 Expires: July 8, 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 . Discussion of this document takes place on the HTTP Working Group mailing list (), which is archived at . Working Group information can be found at . Source for this draft and an issue tracker can be found at . 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 July 8, 2023. Pauly Expires July 8, 2023 [Page 1] Internet-Draft DNS Aliases Proxy-Status January 2023 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 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. 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 Pauly Expires July 8, 2023 [Page 2] Internet-Draft DNS Aliases Proxy-Status January 2023 influence behavior like cookie usage policies [COOKIES] or blocking of malicious hosts. 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. Pauly Expires July 8, 2023 [Page 3] Internet-Draft DNS Aliases Proxy-Status January 2023 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 <>. 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, . [DNS] Barr, D., "Common DNS Operational and Configuration Errors", RFC 1912, DOI 10.17487/RFC1912, February 1996, . [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022, . [PROXY-STATUS] Nottingham, M. and P. Sikora, "The Proxy-Status HTTP Response Header Field", RFC 9209, DOI 10.17487/RFC9209, June 2022, . Pauly Expires July 8, 2023 [Page 4] Internet-Draft DNS Aliases Proxy-Status January 2023 [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, . 5.2. Informative References [COOKIES] Barth, A., "HTTP State Management Mechanism", RFC 6265, DOI 10.17487/RFC6265, April 2011, . Author's Address Tommy Pauly Apple, Inc. Email: tpauly@apple.com Pauly Expires July 8, 2023 [Page 5]