Internet DRAFT - draft-schwartz-modern-http-proxies
draft-schwartz-modern-http-proxies
httpbis B. M. Schwartz
Internet-Draft Google LLC
Intended status: Standards Track 14 October 2022
Expires: 17 April 2023
Modernizing HTTP Forward Proxy Functionality
draft-schwartz-modern-http-proxies-00
Abstract
HTTP proxying features have long been part of the core HTTP
specification. However, the core proxying functionality has several
important deficiencies in modern HTTP environments. This
specification defines alternative proxy service configurations for
HTTP requests and TCP connections. These services are identified by
URI Templates and designed for parallelism with DoH, MASQUE, and
Oblivious HTTP.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 17 April 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. History . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Problems . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Modern HTTP Request Proxies . . . . . . . . . . . . . . . . . 4
3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Modern TCP transport proxies . . . . . . . . . . . . . . . . 5
4.1. In HTTP/1.1 . . . . . . . . . . . . . . . . . . . . . . . 5
4.1.1. Example . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. In HTTP/2 and HTTP/3 . . . . . . . . . . . . . . . . . . 6
5. Additional Examples . . . . . . . . . . . . . . . . . . . . . 7
5.1. Template expansion . . . . . . . . . . . . . . . . . . . 7
5.2. Sample exchanges . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Operational considerations . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
1.1. History
An HTTP forward proxy (or just "proxy" in the HTTP standards) is an
HTTP service that acts on behalf of the client as an intermediary for
some or all HTTP requests. HTTP/1.0 defines the initial HTTP
proxying mechanism: the client formats its request target in
"absolute form" (i.e. with a full URI in the Request-Line) and
delivers it to the proxy, which reissues it to the origin specified
in the URI ([RFC1945], Section 5.1.2). In this specification, we
call this behavior an "HTTP request proxy".
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With the introduction of "https" URIs, a new proxying mechanism was
needed to enable TLS connections to traverse the proxy. To enable
this, HTTP/1.1 introduced the CONNECT method. In this method, the
request target specifies a host and port number, and the proxy
forwards TCP payloads between the client and this destination
([RFC9110], Section 9.3.6). In this specification, we call this
behavior a "TCP transport proxy".
These two methods sufficed until the introduction of HTTP/3, which
uses a UDP transport. The MASQUE effort has filled the gap by
defining proxy mechanisms that are capable of proxying UDP datagrams
[RFC9298], and more generally IP datagrams
[I-D.ietf-masque-connect-ip]. The destination host and port number
(if applicable) are encoded into the HTTP resource path, and end-to-
end datagrams are wrapped into HTTP Datagrams [RFC9297] on the
client-proxy path.
1.2. Problems
Classic HTTP request proxies and TCP transport proxies are identified
by an origin, not a URI. The proxy service does not have a path of
its own. This prevents any origin from hosting multiple distinct
proxy services and makes it difficult to manage a proxy service in a
fashion similar to other HTTP services.
In some circumstances, it may be possible to work around this
limitation by hosting many origins on a single server (virtual-
hosting). In HTTP/1.1, the "Host" header was introduced to support
such virtual-hosting by distinguishing the hostname of the proxy (in
the Host header) from the hostname of the destination (in the
absolute-form request URI). However, in HTTP/2 and HTTP/3, this
distinction no longer exists. As a result, classic HTTP request
proxies are not compatible with virtual-hosting in HTTP/2 or HTTP/3.
Classic TCP transport proxies can be used with a host that is
specified as a domain name or an IP address. However, because only a
single IP address can be specified, Happy Eyeballs and cross-IP
fallback can only be used when the host is a domain name. For
requests to succeed, the client must know which address families are
supported by the proxy.
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1.3. Overview
This specification describes alternative protocols for HTTP request
proxies and TCP transport proxies in HTTP. Like other modern HTTP
access services such as DoH, CONNECT-UDP, and CONNECT-IP, the proxy
is identified by a URI Template. Proxy interactions reuse standard
HTTP components and semantics, avoiding changes to the core HTTP
protocol.
2. Conventions and Definitions
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.
3. Modern HTTP Request Proxies
A modern HTTP request proxy is identified by a URI Template
containing a variable named "target_uri". To convert an HTTP request
into a proxied request, the client MUST substitute the request's URI
into this variable, expand the template, and use the result as the
new request URI.
HTTP headers work the same as in classic HTTP request proxies.
A modern HTTP request proxy is also suitable for use as an Oblivious
HTTP relay, if it provides the required privacy guarantees.
3.1. Example
Consider a proxy identified as "https://example.com/
proxy{?target_uri}". Requests would then be transformed as follows:
Original request:
PATCH /resource HTTP/1.1
Host: api.example
Content-Type: application/example
...
Transformed request:
PATCH /proxy?target_uri=https%3A%2F%2Fapi.example%2Fresource HTTP/1.1
Host: example.com
Content-Type: application/example
Proxy-Authorization: ...
...
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Notes on this example:
* The HTTP method is not altered.
* The request-related headers such as Content-Type are preserved,
but the Host header (or :authority in HTTP/2 and HTTP/3) is
altered.
* Certain characers in the target URI are percent-encoded during URI
Template expansion.
* The scheme, which is implicit in the original request, is explicit
in the transformed request. The scheme in this example is
"https", indicating that the client is asking the proxy to
establish a secure connection to the target.
* The client can add Proxy-* headers to communicate with the proxy.
4. Modern TCP transport proxies
A modern TCP transport proxy for HTTP is identified by a URI Template
[RFC6570] containing variables named "target_host" and "tcp_port".
The client substitutes the destination host and port number into
these variables to produce the request URI.
The "target_host" variable MUST be a domain name, an IP address
literal, or a list of IP addresses. The "tcp_port" variable MUST be
a single integer. If "target_host" is a list (as in Section 2.4.2 of
[RFC6570]), the server SHOULD perform the same connection procedure
as if these addresses had been returned in response to A and AAAA
queries for a domain name.
4.1. In HTTP/1.1
In HTTP/1.1, the client uses the proxy by issuing a request as
follows:
* The method SHALL be "GET".
* The request SHALL include a single Host header field containing
the origin of the proxy.
* The request SHALL include a Connection header field with the value
"Upgrade".
* The request SHALL include an "Upgrade" header field with the value
"connect-tcp".
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* The request's target SHALL be the URI derived from expansion of
the proxy's URI Template.
If the request is well-formed and permissible, the proxy MUST attempt
the TCP connection before returning its response header. If the TCP
connection is successful, the response SHALL be as follows:
* The HTTP status code SHALL be 101 (Switching Protocols).
* The response SHALL include a Connection header field with the
value "Upgrade".
* The response SHALL include a single Upgrade header field with the
value "connect-tcp".
If the request is malformed or impermissible, the proxy MUST return a
4XX error code. If the TCP connection failed, the proxy MUST NOT
return a 101 or 2XX status code.
If the proxy observes an unclean shutdown from the client (e.g. a TCP
RST or TLS error), it SHOULD send a TCP RST to the target. If the
proxy receives a TCP RST from the target, it SHOULD send a TLS
"internal_error" alert to the client, or set the TCP RST bit if TLS
is not in use.
4.1.1. Example
Consider a proxy identified as "https://example.com/
proxy{?target_host,tcp_port}". To establish a TCP connection to
192.0.2.1:443, the following exchange would occur:
Client Proxy
GET /proxy?target_host=192.0.2.1&tcp_port=443 HTTP/1.1
Host: example.com
Connection: Upgrade
Upgrade: connect-tcp
HTTP/1.1 101 Switching Protocols
Connection: Upgrade
Upgrade: connect-tcp
Figure 1: Modern TCP transport proxy in HTTP/1.1
4.2. In HTTP/2 and HTTP/3
In HTTP/2 and HTTP/3, the client uses the proxy by issuing an
"extended CONNECT" request as follows:
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* The :method pseudo-header field SHALL be "CONNECT".
* The :protocol pseudo-header field SHALL be "connect-tcp".
* The :authority pseudo-header field SHALL contain the authority of
the proxy.
* The :path and :scheme pseudo-header fields SHALL contain the path
and scheme of the request URI derived from the proxy's URI
Template.
From this point on, the request and response streams SHALL conform to
all the usual requirements for non-extended CONNECT in this HTTP
version.
5. Additional Examples
5.1. Template expansion
The names of the variables in the URI Template uniquely identify the
capabilities of the proxy. Undefined variables are permitted in URI
Templates, so a single template can be used for multiple purposes:
Combined HTTP request and TCP transport proxy:
https://example.com/proxy{?target_uri,target_host,tcp_port}
Combined HTTP, TCP, UDP, and IP proxy with DoH server:
https://proxy.example/{?target_uri,target_host,tcp_port,port,target,ipproto,dns}
Figure 2: Multipurpose templates
Multipurpose templates can be useful when a single client may benefit
from access to multiple complementary services (e.g. TCP and UDP),
or when the proxy is used by a variety of clients with different
needs.
5.2. Sample exchanges
A modern HTTP request proxy can be used as an Oblivious HTTP Relay.
For example, suppose the relay is identified as
"https://proxy.example.org/relay{?target_uri}", and the Oblivious
HTTP Gateway is "https://example.com/gateway". The client would send
requests to the proxy as follows:
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POST /relay?target_uri=https%3A%2F%2Fexample.com%2Fgateway HTTP/1.1
Host: proxy.example.org
Proxy-Authorization: ...
Content-Type: message/ohttp-req
...
Figure 3: Use of an HTTP request proxy as an Oblivious relay
If a modern HTTP request proxy supports HTTP/2 and Extended CONNECT,
it is even possible to reach a modern TCP transport proxy through it:
CONNECT HTTP/2.0
:authority = request-proxy.example
:scheme = https
:path = /proxy?target_uri=https%3A%2F%2Ftransport-proxy.example%2Fproxy
%3Ftarget_host%3Ddestination.example%26tcp_port%3D443
:protocol = connect-tcp
...
Figure 4: Use of a TCP transport proxy through an HTTP request proxy
Modern TCP transport proxies support requests that offer multiple IP
addresses:
CONNECT HTTP/2.0
:authority = request-proxy.example
:scheme = https
:path = /proxy?target_host=192.0.2.1,2001:db8::1&port=443
:protocol = connect-tcp
...
Figure 5: TCP transport proxy request with multiple IP addresses
6. Security Considerations
None
7. Operational considerations
Modern HTTP proxies can make use of standard HTTP gateways and path-
routing to ease implementation and allow use of shared
infrastructure. However, current gateways might need modifications
to support these services. A compatible gateway must:
* support Extended CONNECT.
* convert HTTP/1.1 Upgrade requests into Extended CONNECT.
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* allow the CONNECT method to pass through to the origin.
* forward Proxy-* request headers to the origin.
8. IANA Considerations
IF APPROVED, IANA is requested to add the following entry to the HTTP
Upgrade Token Registry:
* Value: "connect-tcp"
* Description: Proxying of TCP payloads
* Reference: (This document)
9. References
9.1. 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,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<https://www.rfc-editor.org/rfc/rfc6570>.
[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>.
9.2. Informative References
[I-D.ietf-masque-connect-ip]
Pauly, T., Schinazi, D., Chernyakhovsky, A., Kühlewind,
M., and M. Westerlund, "IP Proxying Support for HTTP",
Work in Progress, Internet-Draft, draft-ietf-masque-
connect-ip-03, 27 September 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-masque-
connect-ip-03>.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945,
DOI 10.17487/RFC1945, May 1996,
<https://www.rfc-editor.org/rfc/rfc1945>.
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[RFC9110] 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>.
[RFC9297] Schinazi, D. and L. Pardue, "HTTP Datagrams and the
Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, August
2022, <https://www.rfc-editor.org/rfc/rfc9297>.
[RFC9298] Schinazi, D., "Proxying UDP in HTTP", RFC 9298,
DOI 10.17487/RFC9298, August 2022,
<https://www.rfc-editor.org/rfc/rfc9298>.
Acknowledgments
TODO acknowledge.
Author's Address
Benjamin M. Schwartz
Google LLC
Email: bemasc@google.com
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