Network Working Group
Captive Portal Interaction                                 T. Pauly, Ed.
Internet-Draft                                                Apple Inc.
Intended status: Standards Track                         D. Thakore, Ed.
Expires: August 7, 2018 January 2, 2019                                       CableLabs
                                                       February 03,
                                                           July 01, 2018

                           Captive Portal API
                       draft-ietf-capport-api-00
                       draft-ietf-capport-api-01

Abstract

   This document describes an HTTP API that allows hosts to interact
   with a Captive Portal system.

Status of This Memo

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   This Internet-Draft will expire on August 7, 2018. January 2, 2019.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Workflow  . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  API Details . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  URI of Captive Portal API endpoint  . . . . . . . . . . .   3
       3.1.1.  Server Authentication . . . . . . . . . . . . . . . .   3
     3.2.  JSON Keys . . . . . . . . . . . . . . . . . . . . . . . .   3   4
     3.3.  Example Exchange  . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4   5
     4.1.  Privacy Considerations  . . . . . . . . . . . . . . . . .   4   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5   7

1.  Introduction

   This document describes a HyperText Transfer Protocol (HTTP)
   Application Program Interface (API) that allows hosts to interact
   with a Captive Portal system.  The API defined in this document has
   been designed to meet the requirements in the Captive Portal
   Architecture [I-D.ietf-capport-architecture].  Specifically, the API
   provides:

   o  The state of captivity (whether or not the host has access to the
      Internet)

   o  A URI that a host's browser can present to a user to get out of
      captivity

   o  An encrypted connection (TLS for both the API and portal URI)

2.  Workflow

   The Captive Portal Architecture defines three steps of interaction
   between hosts and a Captive Portal service:

   1.  Provisioning, in which a host discovers that a network has a
       captive portal, and learns the URI of the API server

   2.  API Server interaction, in which a host queries the state of the
       captive portal and retrieves the necessary information to get out
       of captivity

   3.  Enforcement, in which the enforcement device in the network
       blocks disallowed traffic, and sends ICMP messages to let hosts
       know they are blocked by the captive portal

   This document is focused on the second step.  It is assumed that the
   location of the Captive Portal API server has been discovered by the
   host as part of the first step.  The mechanism for discovering the
   API Server endpoint is not covered by this document.

3.  API Details

3.1.  URI of Captive Portal API endpoint

   The URI of the API endpoint MUST be accessed using HTTP over TLS
   (HTTPS) and SHOULD be served on port 443 [RFC2818].  The host SHOULD
   NOT assume that the URI for a given network attachment will stay the
   same, and SHOULD rely on the discovery or provisioning process each
   time it joins the network.  Depending on how the Captive Portal
   system is configured, the URI may be unique for each host and between
   sessions for the same host.

   For example, if the Captive Portal API server is hosted at
   example.org, the URI's of the API could be:

   o  "https://example.org/captive-portal/api"

   o  "https://example.org/captive-portal/api/X54PD"

3.1.1.  Server Authentication

   The purpose of accessing the Captive Portal API over an HTTPS
   connection is twofold: first, the encrypted connection protects the
   integrity and confidentiality of the API exchange from other parties
   on the local network; and second, it provides the client of the API
   an opportunity to authenticate the server that is hosting the API.
   This authentication is aimed at allowing a user to be reasonably
   confident that the entity providing the Captive Portal API has a
   valid certificate for the hostname in the URI (such as
   "example.com").  The hostname of the API SHOULD be displayed to the
   user in order to indicate the entity which is providing the API
   service.

   Clients performing revocation checking will need some means of
   accessing revocation information for certificates presented by the
   API server.  Online Certificate Status Protocol [RFC6960] (OCSP)
   stapling, using the TLS Certificate Status Request extension
   [RFC6066] SHOULD be used.  OCSP stapling allows a client to perform
   revocation checks without initiating new connections.  To allow for
   other forms of revocation checking, a captive network could permit
   connections to OCSP responders or Certificate Revocation Lists (CRLs)
   that are referenced by certificates provided by the API server.

   Certificates with missing intermediate certificates that rely on
   clients validating the certificate chain using the URI specified in
   the Authority Information Access (AIA) extension [RFC5280] SHOULD NOT
   be used by the Captive Portal API server.  If the certificates do
   require the use of AIA, the captive network will need to allow client
   access to the host specified in the URI.

   If the client is unable to validate the certificate presented by the
   API server, it MUST NOT proceed with any of the behavior for API
   interaction described in this document.  The client will proceed to
   interact with the captive network as if the API capabilities were not
   present.  It may still be possible for the user to access the network
   by being redirected to a web portal.

3.2.  JSON Keys

   The Captive Portal API data structures are specified in JavaScript
   Object Notation (JSON) [RFC7159].  Requests and responses for the
   Captive Portal API use the "application/captive+json" media type.
   Clients SHOULD include this media type as an Accept header in their
   GET requests, and servers MUST mark this media type as their Content-
   Type header in responses.

   The following keys are defined at the top-level of the JSON structure
   returned by the API server:

   o  "permitted" (required, boolean): indicates whether or not the
      Captive Portal is open to the requesting host

   o  "hmac-key" (required, string): provides a per-host key that can be
      used to authenticate messages from the Captive Portal enforcement
      server

   o  "user-portal-url" (required, string): provides the URL of a web
      portal that can be presented to a user to interact with

   o  "expire-date" (optional, string formatted as [RFC3339] datetime):
      indicates the date and time after which the host will be in a
      captive state

   o  "bytes-remaining" (optional, integer): indicates the number of
      bytes left, after which the host will be in a captive state

   Note that the use of the hmac-key is not defined in this document,
   but is intended for use in the enforcement step of the Captive Portal
   Architecture.

3.3.  Example Exchange

   To request the Captive Portal JSON content, a host sends an HTTP GET
   request:

   GET /captive-portal/api/X54PD
   Host: example.org
   Accept: application/json application/captive+json

   The server then responds with the JSON content for that client:

   HTTP/1.1 200 OK
   Cache-Control: private
   Date: Mon, 04 Dec 2013 05:07:35 GMT
   Content-Type: application/json application/captive+json

   {
      "permitted": false,
   "hmac-key": "7cec81acce3176b262a46363666a01881b0e3bf60d97a98b5409b71cc60a1ac0"
      "user-portal-url": "https://example.org/portal.html"
      "expire-date": "2014-01-01T23:28:56.782Z"
   }

4.  Security Considerations

   TBD: Provide complete security requirements and analysis.

4.1.  Privacy Considerations

   Information passed in this protocol may include a user's personal
   information, such as a full name and credit card details.  Therefore,
   it is important that Captive Portal API Servers do not allow access
   to the Captive Portal API over unecrypted unencrypted sessions.

5.  IANA Considerations

   TBD:

   This document registers the media type for Captive Portal API JSON
   text, "application/captive+json".

   Type name:  application

   Subtype name:  captive+json

   Required parameters:  None

   Optional parameters:  None

   Encoding considerations:  Encoding considerations are identical to
      those specified for the "application/json" media type.

   Security considerations:  See Section 4
   Interoperability considerations:  This document specifies format of
      conforming messages and the interpretation thereof.

   Published specification:  This document

   Applications that use this media type:  This media type is intended
      to be used by servers presenting the Captive Portal API, and
      clients connecting to such captive networks.

   Additional information:  None

   Person & email address to contact for further information:  See
      Authors' Addresses section.

   Intended usage:  COMMON

   Restrictions on usage:  None

   Author:  CAPPORT IETF WG

   Change controller:  IETF

6.  Acknowledgments

   This work in this document was started by Mark Donnelly and Margaret
   Cullen.  Thanks to everyone in the CAPPORT Working Group who has
   given input.

7.  References

7.1.  Normative References

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              DOI 10.17487/RFC5785, April 2010,
              <https://www.rfc-editor.org/info/rfc5785>.

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066,
              DOI 10.17487/RFC6066, January 2011,
              <https://www.rfc-editor.org/info/rfc6066>.

   [RFC6960]  Santesson, S., Myers, M., Ankney, R., Malpani, A.,
              Galperin, S., and C. Adams, "X.509 Internet Public Key
              Infrastructure Online Certificate Status Protocol - OCSP",
              RFC 6960, DOI 10.17487/RFC6960, June 2013,
              <https://www.rfc-editor.org/info/rfc6960>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

7.2.  Informative References

   [I-D.ietf-capport-architecture]
              Larose, K. and D. Dolson, "CAPPORT Architecture", draft-
              ietf-capport-architecture-00
              ietf-capport-architecture-02 (work in progress), September
              2017. June
              2018.

Authors' Addresses

   Tommy Pauly (editor)
   Apple Inc.
   1 Infinite Loop
   Cupertino, California 95014
   United States of America

   Email: tpauly@apple.com

   Darshak Thakore (editor)
   CableLabs
   858 Coal Creek Circle
   Louisville, CO 80027
   United States of America

   Email: d.thakore@cablelabs.com