Network Working Group                                           T. Pauly
Internet-Draft                                                Apple Inc.
Intended status: Experimental                                D. Schinazi
Expires: 3 April 2022                                         Google LLC
                                                       30 September 2021


                      The Geohash HTTP Client Hint
                  draft-pauly-httpbis-geohash-hint-00

Abstract

   This documents defines an HTTP Client Hint for sharing a client's
   rough location using the Geohash format.

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

   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 3 April 2022.

Copyright Notice

   Copyright (c) 2021 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



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   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.  Geohash Header  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Server Behavior . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Proxy Behavior  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  HTTP Headers  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   HTTP Client Hints [RFC8942] defines a convention for HTTP headers to
   communicate optional information from clients to servers as hints.
   This can be done conditionally based on if a server claims supports
   for a particular hint.

   This document defines a client hint that can be used to send a
   location that the client wants to use for influencing server
   behavior.  It uses the Geohash algorithm [GEOHASH] to encode latitude
   and longitude coordinates into an alphanumeric token that can be
   truncated to provide a less specific location.

   This header is intended to be used to provide rough geolocation hints
   to servers in situations where the server cannot directly ascertain
   the location of the client.  For example, a client that is accessing
   a server through a proxy or a VPN might provide a rough hint to a
   server when looking up information that may vary depending on
   location.

   This document also defines a how forward proxies can use proxy status
   fields to inform clients about the result of their Geohash hints.









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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.  Geohash Header

   The "Sec-CH-Geohash" is an Item Structured Header [RFC8941].  Its
   value MUST be a String, and MUST have at least 1 character and no
   more than 12 characters.  The ABNF is:

      Sec-CH-Geohash = sf-string

   The string itself is an encoded Geohash, which uses the 32 different
   characters from the "Geohash alphabet" [GEOHASH].

   The following example shows an encoding of the coordinates
   57.64911,10.40744:

       Sec-CH-Geohash: "u4pruydqqvj"

   Servers that can provide different content based on Geohash hints
   SHOULD include the headers in their "Accept-CH" list.

       Accept-CH: Sec-CH-Geohash

   Servers also SHOULD indicate for any cacheable content if the Geohash
   hint will influence the cached content, using the "Vary" header.

       Vary: Sec-CH-Geohash

3.  Server Behavior

   Upon receiving a Geohash Client Hint, a server can use the
   information to influence its behavior in various ways.

   The server can use the Geohash to determine the content of HTTP
   responses, as a replacement for inferring location from client IP
   addresses.

   If the server is acting as a forward proxy, such as a CONNECT proxy,
   it can use the Geohash to determine an appropriate geo-mapped IP
   address to use for outbound connections, or a client subnet to
   present in the EDNS0 Client Subnet extension for DNS queries
   [RFC6891] [RFC7871].



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3.1.  Proxy Behavior

   If a proxy receiving the Geohash hint cannot respect the location
   indicated by the hint, it SHOULD include a Proxy-Status header
   [I-D.ietf-httpbis-proxy-status] in its response, with the "details"
   parameter containing the string "invalid geohash".

   Proxy-Status: ExampleProxy; details="invalid geohash"

4.  Security Considerations

   The use of the Geohash Client Hint MUST use the Sec- header prefix as
   recommended in [RFC8942].

   Client location can be used to fingerprint and tracker users, so
   clients MUST have a default policy around when to allow use of the
   Geohash Client Hint, as well as a default length of Geohash.
   Shorter, truncated Geohashes provide less specific locality.

   Servers MUST NOT use Geohash Client Hints for making security or
   access-control decisions, as the value can be spoofed by a client.
   The hint is intended only for use in optimizing behavior.

5.  IANA Considerations

5.1.  HTTP Headers

   This document registers the "Sec-CH-Geohash" header in the "Permanent
   Message Header Field Names" registry
   <https://www.iana.org/assignments/message-headers>.

     +----------------------+----------+--------+---------------+
     | Header Field Name    | Protocol | Status |   Reference   |
     +----------------------+----------+--------+---------------+
     | Sec-CH-Geohash       |   http   |  exp   | This document |
     +----------------------+----------+--------+---------------+

6.  References

6.1.  Normative References

   [I-D.ietf-httpbis-proxy-status]
              Nottingham, M. and P. Sikora, "The Proxy-Status HTTP
              Response Header Field", Work in Progress, Internet-Draft,
              draft-ietf-httpbis-proxy-status-06, 16 August 2021,
              <https://www.ietf.org/archive/id/draft-ietf-httpbis-proxy-
              status-06.txt>.




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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/info/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/info/rfc8174>.

   [RFC8941]  Nottingham, M. and P-H. Kamp, "Structured Field Values for
              HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
              <https://www.rfc-editor.org/info/rfc8941>.

   [RFC8942]  Grigorik, I. and Y. Weiss, "HTTP Client Hints", RFC 8942,
              DOI 10.17487/RFC8942, February 2021,
              <https://www.rfc-editor.org/info/rfc8942>.

6.2.  Informative References

   [GEOHASH]  "Geohash", 2020, <https://en.wikipedia.org/wiki/Geohash>.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,
              <https://www.rfc-editor.org/info/rfc6891>.

   [RFC7871]  Contavalli, C., van der Gaast, W., Lawrence, D., and W.
              Kumari, "Client Subnet in DNS Queries", RFC 7871,
              DOI 10.17487/RFC7871, May 2016,
              <https://www.rfc-editor.org/info/rfc7871>.

Authors' Addresses

   Tommy Pauly
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014,
   United States of America

   Email: tpauly@apple.com


   David Schinazi
   Google LLC

   Email: dschinazi.ietf@gmail.com





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