Communicating Proxy Configurations in Provisioning Domains
draft-pauly-intarea-proxy-config-pvd-02

Network Working Group                                           T. Pauly
Internet-Draft                                               Apple, Inc.
Intended status: Standards Track                           D. Damjanovic
Expires: 3 September 2024                                      Microsoft
                                                            2 March 2024

       Communicating Proxy Configurations in Provisioning Domains
                draft-pauly-intarea-proxy-config-pvd-02

Abstract

   This document defines a mechanism for accessing provisioning domain
   information associated with a proxy, such as other proxy URIs that
   support different protocols and a list of DNS zones that are
   accessible via a proxy.

Discussion Venues

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

   Source for this draft and an issue tracker can be found at
   https://github.com/tfpauly/privacy-proxy.

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 3 September 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Background  . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Fetching PvD Additional Information for proxies . . . . . . .   4
   3.  Enumerating proxies within a PvD  . . . . . . . . . . . . . .   5
     3.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Split DNS information for proxies . . . . . . . . . . . . . .   8
     4.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Discovering proxies from network PvDs . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  New PvD Additional Information key  . . . . . . . . . . .   9
     7.2.  New PvD Proxy Information Registry  . . . . . . . . . . .  10
     7.3.  New PvD Proxy Protocol Registry . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   HTTP proxies that use the CONNECT method Section 9.3.6 of [HTTP]
   (often referred to as "forward" proxies) allow clients to open
   connections to hosts via a proxy.  These typically allow for TCP
   stream proxying, but can also support UDP proxying [CONNECT-UDP] and
   IP packet proxying [CONNECT-IP].  Such proxies are not just defined
   as hostnames and ports, but can use URI templates [URITEMPLATE].

   In order to make use of multiple related proxies, clients need a way
   to understand which proxies are associated with one another.

   Client can also benefit from learning about additional information
   associated with the proxy to optimize their proxy usage, such knowing
   that a proxy is configured to only allow access to a limited set of
   next hops.

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   These improvements to client behavior can be achieved through the use
   of Provisioning Domains.  Provisioning Domains (PvDs) are defined in
   [PVD] as consistent sets of network configuration information, which
   can include proxy configuration details Section 2 of [PVD].
   [PVDDATA] defines a JSON [JSON] format for describing Provisioning
   Domain Additional Information, which is an extensible dictionary of
   properties of the Provisioning Domain.

   This document defines several mechanisms to use PvDs to help clients
   understand how to use proxies:

   1.  A way to fetch PvD Additional Information associated with a known
       proxy URI (Section 2)

   2.  A way to list one or more proxy URIs in a PvD, allowing clients
       to learn about other proxy options given a known proxy
       (Section 3).

   3.  A way to define a limited set of DNS zones that are accessible
       through the proxy (Section 4).

   Additionally, this document partly describes how these mechanisms
   might be used to discover proxies associated with a network
   (Section 5).

1.1.  Background

   Other non-standard mechanisms for proxy configuration and discovery
   have been used historically, some of which are described in
   [RFC3040].

   Proxy Auto Configuration (PAC) files Section 6.2 of [RFC3040] are
   Javascript scripts that take URLs as input and provide an output of a
   proxy configuration to use.

   Web Proxy Auto-Discovery Protocol (WPAD) Section 6.4 of [RFC3040]
   allows networks to advertise proxies to use by advertising a PAC
   file.  This solution squats on DHCP option 252.

   These common (but non-standard) mechanisms only support defining
   proxies by hostname and port, and do not support configuring a full
   URI template [URITEMPLATE].

   The mechanisms defined in this document are intended to offer a
   standard alternative that works for URI-based proxies and avoids
   dependencies on executing Javascript scripts, which can open up
   security vulnerabilities.

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1.2.  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.  Fetching PvD Additional Information for proxies

   This document defines a way to fetch PvD Additional Information
   associated with a proxy.  This PvD describes the properties of the
   network accessible through the proxy.

   In order to fetch PvD Additional Information associated with a proxy,
   a client issues an HTTP GET request for the well-known PvD URI
   (".well-known/pvd") [PVDDATA] and the host authority of the proxy.
   This is applicable for both proxies that are identified by a host and
   port only (such as SOCKS proxies and HTTP CONNECT proxies) and
   proxies that are identified by a URI or URI template.

   For example, a client would issue the following request for the PvD
   associated with "https://proxy.example.org/
   masque{?target_host,target_port}":

   :method = GET
   :scheme = https
   :authority = proxy.example.org
   :path = /.well-known/pvd
   accept = application/pvd+json

   For a HTTP CONNECT proxy on "proxy.example.org:8080", the client
   would send the following request:

   :method = GET
   :scheme = https
   :authority = proxy.example.org:8080
   :path = /.well-known/pvd
   accept = application/pvd+json

   Note that all proxies that are colocated on the same host and port
   share the same PvD Additional Information.  Proxy deployments that
   need separate PvD configuration properties SHOULD use different
   hosts.

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   PvD Additional Information is required to contain the "identifier",
   "expires", and "prefixes" keys.  For proxy PvDs as defined in this
   document, the "identifier" MUST match the hostname of the HTTP proxy.
   The "prefixes" array SHOULD be empty by default.

3.  Enumerating proxies within a PvD

   This document defines a new PvD Additional Information key, proxies,
   that is an array of dictionaries, where each dictionary in the array
   defines a single proxy that is available as part of the PvD (see
   Section 7.1).  Each proxy is defined by a proxy protocol, a proxy
   location (i.e., a hostname and port or a URI template [URITEMPLATE]),
   along with potentially other keys.

   This document defines two mandatory keys for the sub-dictionaries in
   the proxies array, protocol and proxy.  These keys, defined below,
   are the initial contents of the proxy information key registry
   (Section 7.2).  Other optional keys can be added to the dictionary to
   further define or restrict the use of a proxy.  Clients that do not
   recognize or understand a key in a proxy sub-dictionary MUST ignore
   the entire proxy definition, since the proxy might be only applicable
   for particular uses.

   +========+==============+======+===================================+
   |JSON Key| Description  |Type  | Example                           |
   +========+==============+======+===================================+
   |protocol| The protocol |String| "connect-udp"                     |
   |        | used to      |      |                                   |
   |        | communicate  |      |                                   |
   |        | with the     |      |                                   |
   |        | proxy        |      |                                   |
   +--------+--------------+------+-----------------------------------+
   |proxy   | String       |String| "https://proxy.example.org:4443/  |
   |        | containing   |      | masque{?target_host,target_port}" |
   |        | the URI      |      |                                   |
   |        | template or  |      |                                   |
   |        | hostname and |      |                                   |
   |        | port of the  |      |                                   |
   |        | proxy,       |      |                                   |
   |        | depending on |      |                                   |
   |        | the format   |      |                                   |
   |        | defined by   |      |                                   |
   |        | the protocol |      |                                   |
   +--------+--------------+------+-----------------------------------+

                                 Table 1

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   The values for the protocol key are defined in the proxy protocol
   registry (Section 7.3).  For consistency, any new proxy types that
   use HTTP Upgrade Tokens (and use the :protocol pseudo-header) SHOULD
   define the protocol value to match the Upgrade Token / :protocol
   value.

   +===============+===============+===============+===================+
   | Proxy         | Proxy         | Reference     | Notes             |
   | Protocol      | Location      |               |                   |
   |               | Format        |               |                   |
   +===============+===============+===============+===================+
   | socks5        | hostname:port | [SOCKSv5]     |                   |
   +---------------+---------------+---------------+-------------------+
   | http-connect  | hostname:port | Section 9.3.6 | Standard CONNECT  |
   |               |               | of [HTTP]     | method, using     |
   |               |               |               | unencrypted HTTP  |
   |               |               |               | to the proxy      |
   +---------------+---------------+---------------+-------------------+
   | https-connect | hostname:port | Section 9.3.6 | Standard CONNECT  |
   |               |               | of [HTTP]     | method, using     |
   |               |               |               | TLS-protected     |
   |               |               |               | HTTP to the       |
   |               |               |               | proxy             |
   +---------------+---------------+---------------+-------------------+
   | connect-udp   | URI template  | [CONNECT-UDP] |                   |
   +---------------+---------------+---------------+-------------------+
   | connect-ip    | URI template  | [CONNECT-IP]  |                   |
   +---------------+---------------+---------------+-------------------+
   | connect-tcp   | URI template  | [CONNECT-TCP] |                   |
   +---------------+---------------+---------------+-------------------+

                                  Table 2

   The value of proxy depends on the Proxy Location Format defined by
   proxy protocol.  The types defined here either use a hostname and
   port, or a full URI template.

   When a PvD that contains the proxies key is fetched from a known
   proxy using the method described in Section 2 the proxies list
   describes equivalent proxies (potentially supporting other protocols)
   that can be used in addition to the known proxy.

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   Such cases are useful for informing clients of related proxies as a
   discovery method, with the assumption that the client already is
   aware of one proxy.  Many historical methods of configuring a proxy
   only allow configuring a single FQDN hostname for the proxy.  A
   client can attempt to fetch the PvD information from the well-known
   URI to learn the list of complete URIs that support non-default
   protocols, such as [CONNECT-UDP] and [CONNECT-IP].

3.1.  Example

   Given a known HTTP CONNECT proxy FQDN, "proxy.example.org", a client
   could request PvD Additional Information with the following request:

   :method = GET
   :scheme = https
   :authority = proxy.example.org
   :path = /.well-known/pvd
   accept = application/pvd+json

   If the proxy has a PvD definition for this FQDN, it would return the
   following response to indicate a PvD that has two related proxy URIs.

:status = 200
content-type = application/pvd+json
content-length = 222

{
  "identifier": "proxy.example.org.",
  "expires": "2023-06-23T06:00:00Z",
  "prefixes": [],
  "proxies": [
    {
      "protocol": "http-connect",
      "proxy": "proxy.example.org:80"
    },
    {
      "protocol": "connect-udp",
      "proxy": "https://proxy.example.org/masque{?target_host,target_port}"
    }
  ]
}

   The client would learn the URI template of the proxy that supports
   UDP using [CONNECT-UDP], at "https://proxy.example.org/
   masque{?target_host,target_port}".

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4.  Split DNS information for proxies

   Split DNS configurations are cases where only a subset of domains is
   routed through a VPN tunnel or a proxy.  For example, IKEv2 defines
   split DNS configuration in [IKEV2SPLIT].

   PvD Additional Information can be used to indicate that a proxy PvD
   has a split DNS configuration.

   Section 4.3 of [PVDDATA] defines the optional dnsZones key, which
   contains searchable and accessible DNS zones as an array of strings.

   When present in a PvD Additional Information dictionary that is
   retrieved for a proxy as described in Section 2, domains in the
   dnsZones array indicate specific zones that are accessible using the
   proxy.  If a hostname is not included in the enumerated zones, then a
   client SHOULD assume that the hostname will not be accessible through
   the proxy.

   Entries listed in dnsZones MUST NOT expand the set of domains that a
   client is willing to send to a particular proxy.  The list can only
   narrow the list of domains that the client is willing to send through
   the proxy.  For example, if the client has a local policy to only
   send requests for "example.com" to a proxy "proxy.example.com", and
   the dnsZones array contains "internal.example.com" and
   "other.company.com", the client would end up only proxying
   "internal.example.com" through the proxy.

4.1.  Example

   Given a proxy URI template "https://proxy.example.org/
   masque{?target_host,target_port}", which in this case is for UDP
   proxying, the client could request PvD additional information with
   the following request:

   :method = GET
   :scheme = https
   :authority = proxy.example.org
   :path = /.well-known/pvd
   accept = application/pvd+json

   If the proxy has a PvD definition for this proxy, it could return the
   following response to indicate a PvD that has one accessible zone,
   "internal.example.org".

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   :status = 200
   content-type = application/pvd+json
   content-length = 135

   {
     "identifier": "proxy.example.org.",
     "expires": "2023-06-23T06:00:00Z",
     "prefixes": [],
     "dnsZones": ["internal.example.org"]
   }

   The client could then choose to use this proxy only for accessing
   names that fall within the "internal.example.org" zone.

5.  Discovering proxies from network PvDs

   [PVDDATA] defines how PvD Additional Information is discovered based
   on network advertisements using Router Advertisements [RFC4861].  A
   network defining its configuration via PvD information can include
   the proxies key (Section 3) to inform clients of a list of proxies
   available on the network.

   This association of proxies with the network's PvD can be used as a
   mechanism to discover proxies, as an alternative to PAC files.
   However, client systems MUST NOT automatically send traffic over
   proxies advertised in this way without explicit configuration,
   policy, or user permission.  For example, a client can use this
   mechanism to choose between known proxies, such as if the client was
   already proxying traffic and has multiple options to choose between.

   Further security and experience considerations are needed for these
   cases.

6.  Security Considerations

   Configuration advertised via PvD Additional Information, such DNS
   zones or associated proxies, can only be safely used when fetched
   over a secure TLS-protected connection, and the client has validated
   that that the hostname of the proxy, the identifier of the PvD, and
   the validated hostname identity on the certificate all match.

7.  IANA Considerations

7.1.  New PvD Additional Information key

   This document registers a new key in the "Additional Information PvD
   Keys" registry.

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   JSON Key: proxies

   Description: Array of proxy dictionaries associated with this PvD

   Type: Array of dictionaries

   Example: [ { "protocol": "connect-udp", "proxy":
   "https://proxy.example.org/masque{?target_host,target_port}" } ]

7.2.  New PvD Proxy Information Registry

   IANA is requested to create a new registry "Proxy Information PvD
   Keys", within the "Provisioning Domains (PvDs)" registry page.  This
   new registry reserves JSON keys for use in sub-dictionaries under the
   proxies key.  The initial contents of this registry are given in
   Section 3.

   The status of a key as mandatory or optional is intentionally not
   denoted in the table to allow for flexibility in future use cases.
   Any new assignments of keys will be considered as optional for the
   purpose of the mechanism described in this document.

   New assignments in the "Proxy Information PvD Keys" registry will be
   administered by IANA through Expert Review [RFC8126].  Experts are
   requested to ensure that defined keys do not overlap in names or
   semantics.

7.3.  New PvD Proxy Protocol Registry

   IANA is requested to create a new registry "Proxy Protocol PvD
   Values", within the "Provisioning Domains (PvDs)" registry page.
   This new registry reserves JSON values for the protocol key in
   proxies sub-dictionaries.  The initial contents of this registry are
   given in Section 3.

   New assignments in the "Proxy Protocol PvD Values" registry will be
   administered by IANA through Expert Review [RFC8126].  Experts are
   requested to ensure that defined keys do not overlap in names or
   semantics, and have clear format definitions.  The reference and
   notes fields MAY be empty.

8.  References

8.1.  Normative References

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   [CONNECT-IP]
              Pauly, T., Ed., Schinazi, D., Chernyakhovsky, A.,
              Kühlewind, M., and M. Westerlund, "Proxying IP in HTTP",
              RFC 9484, DOI 10.17487/RFC9484, October 2023,
              <https://www.rfc-editor.org/rfc/rfc9484>.

   [CONNECT-TCP]
              Schwartz, B. M., "Template-Driven HTTP CONNECT Proxying
              for TCP", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-connect-tcp-02, 7 December 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              connect-tcp-02>.

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

   [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>.

   [JSON]     Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/rfc/rfc8259>.

   [PVDDATA]  Pfister, P., Vyncke, É., Pauly, T., Schinazi, D., and W.
              Shao, "Discovering Provisioning Domain Names and Data",
              RFC 8801, DOI 10.17487/RFC8801, July 2020,
              <https://www.rfc-editor.org/rfc/rfc8801>.

   [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>.

   [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/rfc/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/rfc/rfc8174>.

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   [SOCKSv5]  Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
              L. Jones, "SOCKS Protocol Version 5", RFC 1928,
              DOI 10.17487/RFC1928, March 1996,
              <https://www.rfc-editor.org/rfc/rfc1928>.

   [URITEMPLATE]
              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>.

8.2.  Informative References

   [IKEV2SPLIT]
              Pauly, T. and P. Wouters, "Split DNS Configuration for the
              Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 8598, DOI 10.17487/RFC8598, May 2019,
              <https://www.rfc-editor.org/rfc/rfc8598>.

   [PVD]      Anipko, D., Ed., "Multiple Provisioning Domain
              Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
              <https://www.rfc-editor.org/rfc/rfc7556>.

   [RFC3040]  Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
              Replication and Caching Taxonomy", RFC 3040,
              DOI 10.17487/RFC3040, January 2001,
              <https://www.rfc-editor.org/rfc/rfc3040>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/rfc/rfc4861>.

Authors' Addresses

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

   Dragana Damjanovic
   Microsoft
   Email: ddamjanovic@microsoft.com

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