rfc9532.original   rfc9532.txt 
HTTP T. Pauly Internet Engineering Task Force (IETF) T. Pauly
Internet-Draft Apple, Inc. Request for Comments: 9532 Apple, Inc.
Intended status: Standards Track 13 December 2023 Category: Standards Track January 2024
Expires: 15 June 2024 ISSN: 2070-1721
HTTP Proxy-Status Parameter for Next-Hop Aliases HTTP Proxy-Status Parameter for Next-Hop Aliases
draft-ietf-httpbis-alias-proxy-status-07
Abstract Abstract
This document defines the next-hop-aliases HTTP Proxy-Status This document defines the next-hop-aliases HTTP Proxy-Status
Parameter. This parameter carries the list of aliases and canonical Parameter. This parameter carries the list of aliases and canonical
names an intermediary received during DNS resolution as part of names an intermediary received during DNS resolution as part of
establishing a connection to the next hop. 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 Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
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
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
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Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 15 June 2024. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9532.
Copyright Notice Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements
2. next-hop-aliases Parameter . . . . . . . . . . . . . . . . . 3 2. next-hop-aliases Parameter
2.1. Encoding special characters . . . . . . . . . . . . . . . 4 2.1. Encoding Special Characters
3. Implementation Considerations . . . . . . . . . . . . . . . . 5 3. Implementation Considerations
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. References
6.1. Normative References . . . . . . . . . . . . . . . . . . 6 6.1. Normative References
6.2. Informative References . . . . . . . . . . . . . . . . . 7 6.2. Informative References
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address
1. Introduction 1. Introduction
The Proxy-Status HTTP response field [PROXY-STATUS] allows The Proxy-Status HTTP response field [PROXY-STATUS] allows
intermediaries to convey information about how they handled the intermediaries to convey information about how they handled the
request in HTTP responses sent to clients. It defines a set of request in HTTP responses sent to clients. It defines a set of
parameters that provide information, such as the name of the next parameters that provide information, such as the name of the next
hop. hop.
[PROXY-STATUS] defines a next-hop parameter, which can contain a [PROXY-STATUS] defines a next-hop parameter, which can contain a
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the next hop. the next hop.
Knowing the full chain of names that were used during DNS resolution Knowing the full chain of names that were used during DNS resolution
via CNAME records [DNS] is particularly useful for clients of forward via CNAME records [DNS] is particularly useful for clients of forward
proxies, in which the client is requesting to connect to a specific proxies, in which the client is requesting to connect to a specific
target hostname using the CONNECT method [HTTP] or UDP proxying target hostname using the CONNECT method [HTTP] or UDP proxying
[CONNECT-UDP]. CNAME records can be used to "cloak" hosts that [CONNECT-UDP]. CNAME records can be used to "cloak" hosts that
perform tracking or malicious activity behind more innocuous perform tracking or malicious activity behind more innocuous
hostnames, and clients such as web browsers use the chain of DNS hostnames, and clients such as web browsers use the chain of DNS
names to influence behavior like cookie usage policies [COOKIES] or names to influence behavior like cookie usage policies [COOKIES] or
blocking of malicious hosts. the blocking of malicious hosts.
This document allows clients to receive the CNAME chain of DNS names This document allows clients to receive the CNAME chain of DNS names
for the next hop by including the list of names in a new next-hop- for the next hop by including the list of names in a new next-hop-
aliases Proxy-Status parameter. aliases Proxy-Status parameter.
1.1. Requirements 1.1. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. next-hop-aliases Parameter 2. next-hop-aliases Parameter
The next-hop-aliases parameter's value is a String The value of the next-hop-aliases parameter is a String
[STRUCTURED-FIELDS] that contains one or more DNS names in a comma- [STRUCTURED-FIELDS] that contains one or more DNS names in a comma-
separated list. The items in the list include all alias names and separated list. The items in the list include all alias names and
canonical names received in CNAME records [DNS] during the course of canonical names received in CNAME records [DNS] during the course of
resolving the next hop's hostname using DNS, and MAY include the resolving the next hop's hostname using DNS and MAY include the
original requested hostname itself. The names ought to appear in the original requested hostname itself. The names ought to appear in the
order in which they were received in DNS, for the sake of order in which they were received in DNS, for the sake of
consistency. If there are multiple CNAME records in the chain, the consistency. If there are multiple CNAME records in the chain, the
first name in the next-hop-aliases list would be the value in the first name in the next-hop-aliases list would be the value in the
CNAME record for the original hostname, and the final name in the CNAME record for the original hostname, and the final name in the
next-hop-aliases list would be the name that ultimately resolved to next-hop-aliases list would be the name that ultimately resolved to
one or more addresses. one or more addresses.
The list of DNS names in next-hop-aliases uses a comma (",") as a The list of DNS names in next-hop-aliases parameter uses a comma
separator between names. Note that if a comma is included in a name (",") as a separator between names. Note that if a comma is included
itself, the comma must be encoded as described in Section 2.1. in a name itself, the comma must be encoded as described in
Section 2.1.
For example, consider a proxy "proxy.example.net" that receives the For example, consider a proxy "proxy.example.net" that receives the
following records when performing DNS resolution for the next hop following records when performing DNS resolution for the next hop
"host.example.com": "host.example.com":
host.example.com. CNAME tracker.example.com. host.example.com. CNAME tracker.example.com.
tracker.example.com. CNAME service1.example.com. tracker.example.com. CNAME service1.example.com.
service1.example.com. AAAA 2001:db8::1 service1.example.com. AAAA 2001:db8::1
The proxy could include the following proxy status in its response: The proxy could include the following proxy status in its response:
Proxy-Status: proxy.example.net; next-hop="2001:db8::1"; Proxy-Status: proxy.example.net; next-hop="2001:db8::1";
next-hop-aliases="tracker.example.com,service1.example.com" next-hop-aliases="tracker.example.com,service1.example.com"
This indicates that proxy.example.net, which used the IP address This indicates that "proxy.example.net", which used the IP address
"2001:db8::1" as the next hop for this request, encountered the names "2001:db8::1" as the next hop for this request, encountered the names
"tracker.example.com" and "service1.example.com" in the DNS "tracker.example.com" and "service1.example.com" in the DNS
resolution chain. Note that while this example includes both the resolution chain. Note that while this example includes both the
next-hop and next-hop-aliases parameters, next-hop-aliases can be next-hop and next-hop-aliases parameters, next-hop-aliases can be
included without including next-hop. included without including next-hop.
The proxy can also include the name of the next hop as the first item The proxy can also include the name of the next hop as the first item
in the list. This is particularly useful for reverse proxies when in the list. This is particularly useful for reverse proxies when
clients would not otherwise know the name of the next hop, and the clients would not otherwise know the name of the next hop, and the
next-hop header is used to convey an IP address. next-hop header is used to convey an IP address.
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host2.example.com. CNAME service2.example.com. host2.example.com. CNAME service2.example.com.
service2.example.com. AAAA 2001:db8::2 service2.example.com. AAAA 2001:db8::2
The proxy could include the following proxy status in its response: The proxy could include the following proxy status in its response:
Proxy-Status: reverseproxy.example.net; next-hop="2001:db8::2"; Proxy-Status: reverseproxy.example.net; next-hop="2001:db8::2";
next-hop-aliases="host2.example.com,service2.example.com" next-hop-aliases="host2.example.com,service2.example.com"
The next-hop-aliases parameter only applies when DNS was used to 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. resolve the next hop's name, and it does not apply in all situations.
Clients can use the information in this parameter to determine how to Clients can use the information in this parameter to determine how to
use the connection established through the proxy, but need to use the connection established through the proxy, but they need to
gracefully handle situations in which this parameter is not present. gracefully handle situations in which this parameter is not present.
The proxy MAY send the empty string ("") as the value of next-hop- The proxy MAY send the empty string ("") as the value of next-hop-
aliases to indicate that no CNAME records were encountered when aliases parameter to indicate that no CNAME records were encountered
resolving the next hop's name. when resolving the next hop's name.
2.1. Encoding special characters 2.1. Encoding Special Characters
DNS names commonly just contain alphanumeric characters and hyphens DNS names commonly contain just alphanumeric characters and hyphens
("-"), although they are allowed to contain any character ([RFC1035], ("-"), although they are allowed to contain any character ([RFC1035],
Section 3.1), including a comma. To prevent commas or other special Section 3.1), including a comma. To prevent commas or other special
characters in names leading to incorrect parsing, any characters that characters in names leading to incorrect parsing, any characters that
appear in names in this list that do not belong to the set of URI appear in names in this list that do not belong to the set of URI
Unreserved Characters ([RFC3986], Section 2.3) MUST be percent- unreserved characters ([RFC3986], Section 2.3) MUST be percent-
encoded as defined in [RFC3986], Section 2.1. encoded as defined in [RFC3986], Section 2.1.
For example, consider the DNS name comma,name.example.com. This name For example, consider the DNS name "comma,name.example.com". This
would be encoded within a next-hop-aliases parameter as follows: name would be encoded within a next-hop-aliases parameter as follows:
Proxy-Status: proxy.example.net; next-hop="2001:db8::1"; Proxy-Status: proxy.example.net; next-hop="2001:db8::1";
next-hop-aliases="comma%2Cname.example.com,service1.example.com" next-hop-aliases="comma%2Cname.example.com,service1.example.com"
It is also possible for a DNS name to include a period character It is also possible for a DNS name to include a period character
(".") within a label, instead of as a label separator. In this case, (".") within a label instead of as a label separator. In this case,
the period character MUST be first escaped as "\.". Since the "\" the period character MUST first be escaped as "\.". Since the "\"
character itself will be percent-encoded, the name character itself will be percent-encoded, the name
"dot\.label.example.com" would be encoded within a next-hop-aliases "dot\.label.example.com" would be encoded within a next-hop-aliases
parameter as follows: parameter as follows:
Proxy-Status: proxy.example.net; next-hop="2001:db8::1"; Proxy-Status: proxy.example.net; next-hop="2001:db8::1";
next-hop-aliases="dot%5C.label.example.com,service1.example.com" next-hop-aliases="dot%5C.label.example.com,service1.example.com"
Upon parsing this name, "dot%5C.label" MUST be treated as a single Upon parsing this name, "dot%5C.label" MUST be treated as a single
label. label.
Similarly the "\" character in a label MUST be escaped as "\\" and Similarly, the "\" character in a label MUST be escaped as "\\" and
then percent-encoded. Other uses of "\" MUST NOT appear in the label then percent-encoded. Other uses of "\" MUST NOT appear in the label
after percent-decoding. For example, if there is a DNS name after percent-decoding. For example, if there is a DNS name
"backslash\name.example.com", it would first be escaped as "backslash\name.example.com", it would first be escaped as
"backslash\\name.example.com", and then percent-encoded as follows: "backslash\\name.example.com" and then percent-encoded as follows:
Proxy-Status: proxy.example.net; next-hop="2001:db8::1"; Proxy-Status: proxy.example.net; next-hop="2001:db8::1";
next-hop-aliases="backslash%5C%5Cname.example.com,service1.example.com" next-hop-aliases="backslash%5C%5Cname.example.com,s1.example.com"
3. Implementation Considerations 3. Implementation Considerations
In order to include the next-hop-aliases parameter, a proxy needs to In order to include the next-hop-aliases parameter, a proxy needs to
have access to the chain of alias names and canonical names received have access to the chain of alias names and canonical names received
in CNAME records. in CNAME records.
Implementations ought to note that the full chain of names might not Implementations ought to note that the full chain of names might not
be available in common DNS resolution APIs, such as getaddrinfo be available in common DNS resolution APIs, such as getaddrinfo
[POSIX]. getaddrinfo does have an option for AI_CANONNAME [POSIX]. getaddrinfo does have an option for AI_CANONNAME ([RFC3493],
(Section 6.1 of [RFC3493]), but this will only return the last name Section 6.1), but this will only return the last name in the chain
in the chain (the canonical name), not the alias names. (the canonical name), not the alias names.
An implementation MAY include incomplete information in the next-hop- An implementation MAY include incomplete information in the next-hop-
aliases parameter to accommodate cases where it is unable to include aliases parameter to accommodate cases where it is unable to include
the full chain, such as only including the canonical name if the the full chain, such as only including the canonical name if the
implementation can only use getaddrinfo as described above. implementation can only use getaddrinfo as described above.
4. Security Considerations 4. Security Considerations
The next-hop-aliases parameter does not include any DNSSEC The next-hop-aliases parameter does not include any DNSSEC
information or imply that DNSSEC was used. The information included information or imply that DNSSEC was used. The information included
in the parameter can only be trusted to be valid insofar as the in the parameter can only be trusted to be valid insofar as the
client trusts the proxy to provide accurate information. This client trusts the proxy to provide accurate information. This
information is intended to be used as a hint, and SHOULD NOT be used information is intended to be used as a hint and SHOULD NOT be used
for making security decisions about the identity of a resource for making security decisions about the identity of a resource
accessed through the proxy. accessed through the proxy.
Inspecting CNAME chains can be used to detect cloaking of trackers or Inspecting CNAME chains can be used to detect cloaking of trackers or
malicious hosts. However, the CNAME records could be omitted by a malicious hosts. However, the CNAME records could be omitted by a
recursive or authoritative resolver that is trying to hide this form recursive or authoritative resolver that is trying to hide this form
of cloaking. In particular, recursive or authoritative resolvers can of cloaking. In particular, recursive or authoritative resolvers can
omit these records for both clients directly performing DNS name omit these records for both clients directly performing DNS name
resolution and proxies performing DNS name resolution on behalf of resolution and proxies performing DNS name resolution on behalf of a
client. A malicious proxy could also choose to not report these client. A malicious proxy could also choose to not report these
CNAME chains in order to hide the cloaking. In general, clients can CNAME chains in order to hide the cloaking. In general, clients can
trust information included (or not included) in the next-hop-aliases trust information included (or not included) in the next-hop-aliases
parameter to the degree that the proxy and any resolvers used by the parameter to the degree that the proxy and any resolvers used by the
proxy are trusted. proxy are trusted.
5. IANA Considerations 5. IANA Considerations
This document registers the "next-hop-aliases" parameter in the "HTTP This document registers the next-hop-aliases parameter in the "HTTP
Proxy-Status Parameters" registry <https://www.iana.org/assignments/ Proxy-Status Parameters" registry <https://www.iana.org/assignments/
http-proxy-status>. http-proxy-status> as shown in Table 1.
Name: next-hop-aliases
Description: A string containing one or more DNS aliases or +==================+=================================+===========+
canonical names used to establish a proxied connection to the next | Name | Description | Reference |
hop. +==================+=================================+===========+
| next-hop-aliases | A string containing one or more | RFC 9532 |
| | DNS aliases or canonical names | |
| | used to establish a proxied | |
| | connection to the next hop. | |
+------------------+---------------------------------+-----------+
Reference: This document Table 1: HTTP Proxy-Status Parameters Registry
6. References 6. References
6.1. Normative References 6.1. Normative References
[CONNECT-UDP] [CONNECT-UDP]
Schinazi, D., "Proxying UDP in HTTP", RFC 9298, Schinazi, D., "Proxying UDP in HTTP", RFC 9298,
DOI 10.17487/RFC9298, August 2022, DOI 10.17487/RFC9298, August 2022,
<https://www.rfc-editor.org/rfc/rfc9298>. <https://www.rfc-editor.org/info/rfc9298>.
[DNS] Mockapetris, P., "Domain names - concepts and facilities", [DNS] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/rfc/rfc1034>. <https://www.rfc-editor.org/info/rfc1034>.
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110, Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022, DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>. <https://www.rfc-editor.org/info/rfc9110>.
[PROXY-STATUS] [PROXY-STATUS]
Nottingham, M. and P. Sikora, "The Proxy-Status HTTP Nottingham, M. and P. Sikora, "The Proxy-Status HTTP
Response Header Field", RFC 9209, DOI 10.17487/RFC9209, Response Header Field", RFC 9209, DOI 10.17487/RFC9209,
June 2022, <https://www.rfc-editor.org/rfc/rfc9209>. June 2022, <https://www.rfc-editor.org/info/rfc9209>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[STRUCTURED-FIELDS] [STRUCTURED-FIELDS]
Nottingham, M. and P. Kamp, "Structured Field Values for Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>. <https://www.rfc-editor.org/info/rfc8941>.
6.2. Informative References 6.2. Informative References
[COOKIES] Barth, A., "HTTP State Management Mechanism", RFC 6265, [COOKIES] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011, DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/rfc/rfc6265>. <https://www.rfc-editor.org/info/rfc6265>.
[POSIX] IEEE, "Standard for Information Technology Portable [POSIX] IEEE, "IEEE Standard for Information Technology--Portable
Operating System Interface (POSIX(R)) Base Specifications, Operating System Interface (POSIX(TM)) Base
Issue 7", DOI 10.1109/ieeestd.2013.6506091, April 2013, Specifications, Issue 7", IEEE Std 1003.1-2017,
<http://ieeexplore.ieee.org/servlet/ DOI 10.1109/IEEESTD.2018.8277153, January 2018,
opac?punumber=6506089>. <https://ieeexplore.ieee.org/document/8277153>.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/rfc/rfc1035>. November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W. [RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6", Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, DOI 10.17487/RFC3493, February 2003, RFC 3493, DOI 10.17487/RFC3493, February 2003,
<https://www.rfc-editor.org/rfc/rfc3493>. <https://www.rfc-editor.org/info/rfc3493>.
Author's Address Author's Address
Tommy Pauly Tommy Pauly
Apple, Inc. Apple, Inc.
Email: tpauly@apple.com Email: tpauly@apple.com
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