Captive Portal (CAPPORT) API
draft-donnelly-capport-detection-01

Abstract

This document describes an HTTP API that allows User Equipment to detect the existence of a Captive Portal on the local network, determine the properties of the Captive Portal, and satisfy requirements for network access.

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 http://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 September 14, 2017.

Copyright Notice

Copyright (c) 2017 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 (http://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 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. Requirements Notation
• 3. Workflow
• 4. Use of the DHCP Captive-Portal Option
• 5. CAPPORT API
• 5.1. URLs and HTTP Methods
• 5.1.1. Associating User Equipment with its URL
• 5.1.2. Fallback URL
• 5.1.3. CAPPORT API POST URL
• 5.1.4. CAPPORT REST API DELETE URL
• 5.2. JSON Data Structures
• 5.2.1. CAPPORT Common Elements
• 5.2.1.1. Toplevel Object
• 5.2.1.2. Networks Object
• 5.2.1.3. Network Object
• 5.2.1.4. Condition Object
• 5.2.1.5. Session Token Object
• 5.2.2. User Equipment Request
• 5.2.2.1. Satisfaction Details Object
• 5.2.3. CAPPORT API Server Response
• 5.2.3.1. Requirement Details Object
• 5.2.3.2. Network State Object
• 6. Network Access Conditions
• 6.1. Terms and Conditions
• 6.1.1. Requirements
• 6.1.2. Satisfaction
• 6.2. Passcode
• 6.2.1. Requirements
• 6.2.2. Satisfaction
• 7. IANA Considerations
• 8. Security Considerations
• 8.1. Privacy Considerations
• 9. Acknowledgements
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Authors' Addresses

1. Introduction

This document describes a HyperText Transfer Protocol (HTTP) Application Program Interface (API) that allows User Equipment to detect the existence of a Captive Portal (CAPPORT) on the local network, determine the properties of the Captive Portal, and satisfy requirements for network access. The API defined in this document has been designed to meet the requirements of the CAPPORT API, as discussed in the CAPPORT Architecture [I-D.larose-capport-architecture].

2. Requirements Notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. Workflow

The CAPPORT protocol consists of three phases. In the first phase User Equipment acquires an IP address and determines the URL of the local CAPPORT API Server, if any. The second phase consists of the User Equipment querying the CAPPORT API Server for the requirements for accessing its protected networks, and submitting proofs of meeting those requirements. In the third phase, the User Equipment is granted access to the protected network and can query the CAPPORT API Server for status.

During the first phase, User Equipment uses the Dynamic Host Configuration Protocol (DHCP) or IPv6 Router Advertisements (RAs) to acquire an IP address and to determine the URL for the local CAPPORT API Server. This details for the first phase are described in RFC 7710 [RFC7710], and the rest of this document assumes that the User Equipments already has a URL to reach the CAPPORT API Server.

The second phase begins with the User Equipment accessing the URL provided in the first phase. The CAPPORT API Server responds with the current status of the User Equipment's access to the protected networks and any conditions requirements to gain access to the protected networks. The User Equipment then submits proofs of satisfying the access requirements to the CAPPORT API Server. The CAPPORT API Server again responds with the current status of the User Equipment and any additional requirements necessary to gain access to the protected network. The second phase continues until all of the requirements are met; the CAPPORT API Server grants access to the protected network and responds with a status indicating the access.

At any point in the second phase, the User Equipment MAY stop communicating over the CAPPORT protocol and instead direct a web browser to access the URL. The web browser then becomes the agent for proving that the User Equipment meets the requirements for access to the protected networks.

During the third phase, the User Equipment has access to the protected network. The User Equipment may access the URL provided in the first phase to query the current status. The CAPPORT API Server responds with the current status of the User Equipment. The CAPPORT API Server SHOULD respond with the current status of the User Equipment regardless of whether the User Equipment used the automated CAPPORT protocol or a web browser to complete the second phase.

4. Use of the DHCP Captive-Portal Option

As decribed above, to use the CAPPORT API, User Equipment needs a URL that can be used to reach the CAPPORT API Server. DHCP Servers and IPv6 Routers should provide, and User Equipment SHOULD obtain, the required URL using the DCHP Captive-Portal Option or the IPv6 RA Captive-Portal Option, as described in [RFC7710].

To provide backwards compatibility with the original use of the DHCP and RA options described in RFC7710, the CAPPORT API defined in this document is exclusively accessed using HTTP Methods with an Accept header value of "application/json". Captive Portals that implement the CAPPORT API SHOULD respond to an HTTP GET that has an Accept header of "text/html" with HTML content that, when displayed in a web browser, will allow the user to interactively meet the Captive Portal requirements for network access.

5. CAPPORT API

This section defines the CAPPORT API.

5.1. URLs and HTTP Methods

This section describes the URLs that can be used to access the CAPPORT API.

5.1.1. Associating User Equipment with its URL

The CAPPORT API Server SHOULD associate an incoming request with a particular User Equipment consistently. [TODO: specify how this would happen.]

5.1.2. Fallback URL

The CAPPORT API Server SHOULD respond to HTTP GET requests to the provided URL that specify an Accept header value of "text/html" with HTML content instead of this protocol. If the User Equipment determines that it is unable to satisfy the conditions for network access, it SHOULD display this fallback URL in a web browser to allow the user to complete the network access outside of this protocol.

5.1.3. CAPPORT API POST URL

The CAPPORT API Server SHOULD respond to HTTP POST requests to the provided URL that specify an Accept header value of "application/json" with the CAPPORT API protocol.

5.1.4. CAPPORT REST API DELETE URL

The CAPPORT API Server SHOULD respond to HTTP DELETE requests to the provided URL that specify an Accept header value of "application/json" by revoking any network access to protected networks immediately. The CAPPORT API Server MUST NOT allow any device other than the User Equipment to DELETE the network access of the User Equipment via the CAPPORT API.

The CAPPORT API Server MAY delete the session token (Section 5.2.1.5) for this User Equipment as part of the DELETE request.

5.2. JSON Data Structures

The CAPPORT API data structures are specified in JavaScript Object Notation (JSON) [RFC7159]. This document specifies the structure of the JSON structures and message using the JSON Content Rules (JCR) defined in draft-newton-json-content-rules [I-D.newton-json-content-rules].

5.2.1. CAPPORT Common Elements

This section describes structures that are shared between requests and responses.

5.2.1.1. Toplevel Object

The CAPPORT API will contain JSON-formatted data. The toplevel object contains a networks object whose value is an array of zero or more network objects.

    $toplevel = {
      $networks ,
      $session_token ?
    }
                

The toplevel object MUST contain a networks object.

The CAPPORT API Server responses MUST contain a session_token object. The session-token object contains a session token which will be used in ICMP requests as discussed in RFC 7710.

QUESTION: Should the session token just be provided by the server, or should it be negotiated between the client and server using something like a DH exchange?

5.2.1.2. Networks Object

The networks object represents the list of networks being acted on in this CAPPORT session.

    $networks = {
      ( "DEFAULT" || // ) = $network +
    }
                

The networks object is a JSON object whose keys are network names and whose values are network objects. Thus a single response could be used in gaining access to multiple protected networks at once. The first request to the CAPPORT API Server will contain no networks, and acts as a discovery request.

The CAPPORT API Server SHOULD use the special name DEFAULT for one network that provides access to the greater Internet.

5.2.1.3. Network Object

The network object represents a network protected by the Captive Portal.

    $network = {
      "conditions" : [ $condition + ] ,
      "state" : $network_state ? ,
      "details" : $network_details ?
    }
                

The network object MUST contain a 'conditions' key whose value is an array of one or more $condition objects, which represent the unmet conditions for gaining access to this network. The conditions object SHOULD NOT contain conditions that have already been met.

CAPPORT API Server responses MUST contain the 'state' key, whose value is the $network_state object, which represents the state of access that the User Equipment has to the network.

CAPPORT API Server responses SHOULD contain the 'details' key, whose value is the $network_details object, which provides relevant information about the network.

5.2.1.4. Condition Object

The condition object describes one of the conditions necessary for access to the protected network. The CAPPORT API Server uses this object to express the requirements for User Equipment to access the protected network. The User Equipment uses this object as proof that it has satisfied the corresponding requirement for access to the protected network.

    $condition = {
      "id" : $uuid,
      "type" : string ? ,
      "requirement_details" : $requirement_details ? ,
      "satisfaction_details" : $satisfaction_details ?
    }
                

The condition object MUST include an 'id' key whose value is a UUID that uniquely identifies this condition. This ID will be used to match the client condition satisfactions with the server condition requirements.

CAPPORT API Server responses MUST contain the 'type' key, whose value is a string that represents the type of condition that permits access to the network.

CAPPORT API Server responses MUST contain the 'requirement_details' key, whose value is the $requirement_details object. The $requirement_details object details the requirements that the User Equipment must pass to gain access to the protected network.

User Equipment requests MUST contain the 'satisfaction_details' key, whose value is the $satisfaction_details object. The $satisfaction _details object details the proof that the User Equipment has satisfied the conditions of access to the protected network.

5.2.1.5. Session Token Object

The session_token object describes the CAPPORT session token.

    $session_token = "session_token" : base64
                

The session_token object MUST include a "session_token" key whose value is a base64-encoded string of a 32-bit session token. This token will be used as proposed in [I-D.larose-capport-architecture]. The CAPPORT API Server SHOULD send the same session token to a given User Equipment in every response, until the User Equipment DELETEs its network access (Section 5.1.4). After a DELETE, the CAPPORT API Server MAY generate a new session token if the User Equipment makes a new request.

5.2.2. User Equipment Request

For the initial CAPPORT request from the User Equipment, the JSON object will consist of the toplevel object [json_toplevel_object] with its required networks [json_networks_object] and session_token [json_session_token_object] objects. The networks object will contain no networks, and the session_token object will be empty. This acts as a discovery request.

    {
      "networks" : {}
      "session-token" : ""
    }
              

    $satisfaction_details = { // : any + }
              

    $requirement_details = { // : any + }
                

    $network_state = {
      "permitted" : boolean ,
      "expires" : datetime ? ,
      "bytes_remaining" : integer ?
    }
                

    $requirement_details = {
      "text" : string ?,
      "html" : string ?
    }
              

    $satisfaction_details = {
      "text" : string ?,
      "html" : string ?
    }
              

    $requirement_details = { }
              

    $satisfaction_details = {
      "passcode" : string
    }