Captive Portal Interaction T. Pauly, Ed. Internet-Draft Apple Inc. Intended status: Standards Track D. Thakore, Ed. Expires: September 12, 2019 CableLabs March 11, 2019 Captive Portal API draft-ietf-capport-api-02 Abstract This document describes an HTTP API that allows clients to interact with a Captive Portal system. 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 September 12, 2019. Copyright Notice Copyright (c) 2019 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 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. Pauly & Thakore Expires September 12, 2019 [Page 1] Internet-Draft Captive Portal API March 2019 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Workflow . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. API Details . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.1. URI of Captive Portal API endpoint . . . . . . . . . . . 3 4.1.1. Server Authentication . . . . . . . . . . . . . . . . 4 4.2. JSON Keys . . . . . . . . . . . . . . . . . . . . . . . . 4 4.3. An Example Interaction . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 5.1. Privacy Considerations . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction This document describes a HyperText Transfer Protocol (HTTP) Application Program Interface (API) that allows clients 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 client has access to the Internet) o A URI that a client browser can present to a user to get out of captivity o An encrypted connection (TLS for both the API and portal URI) 2. Terminology This document leverages the terminology and components described in [I-D.ietf-capport-architecture] and additionally uses the following association: o Captive Portal Client: The client that interacts with the captive portal API is typically some application running on the User Equipment that is connected to the Captive Network. This is also referred to as the "client" in this document. Pauly & Thakore Expires September 12, 2019 [Page 2] Internet-Draft Captive Portal API March 2019 o Captive Portal API Server: The server exposing the API's defined in this document to the client. This is also referred to as the "API server" in this document. 3. Workflow The Captive Portal Architecture defines three steps of interaction between clients and a Captive Portal service: 1. Provisioning, in which a client discovers that a network has a captive portal, and learns the URI of the API server 2. API Server interaction, in which a client 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 clients 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 client as part of the first step. The mechanism for discovering the API Server endpoint is not covered by this document. 4. API Details 4.1. 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 client 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 might be unique for each client host and between sessions for the same client 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" Pauly & Thakore Expires September 12, 2019 [Page 3] Internet-Draft Captive Portal API March 2019 4.1.1. 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. In addition to connections to OCSP responders and CRLs, a captive network SHOULD also permit connections to Network Time Protocol (NTP) [RFC5905] servers or other time-sync mechnisms to allow clients to accurately validate certificates. 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. 4.2. 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 Pauly & Thakore Expires September 12, 2019 [Page 4] Internet-Draft Captive Portal API March 2019 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 "captive" (required, boolean): indicates whether the client is in a state of captivity, i.e it has not satisfied the conditions to access the external network. If the client is captive (i.e. captive=true), it can still be allowed enough access for it to perform server authentication Section 4.1.1. o "user-portal-url" (required, string): provides the URL of a web portal with which a user can interact. o "vendor-info-url" (optional, string): provides the URL of a webpage or site on which the operator of the network has information that it wishes to share with the user (e.g. store info, maps, flight status, or entertainment). o "expire-date" (optional, string formatted as [RFC3339] datetime): indicates the date and time after which the client will be in a captive state. The API server SHOULD include this value if the client is not captive (i.e. captive=false) and SHOULD omit this value for captive clients. o "bytes-remaining" (optional, integer): indicates the number of bytes remaining, after which the client will be in placed into a captive state. 4.3. An Example Interaction A client connected to a captive network upon discovering the URI of the API server will query the API server to retrieve information about its captive state and conditions to escape captivity. To request the Captive Portal JSON content, a client sends an HTTP GET request: GET /captive-portal/api/X54PD Host: example.org Accept: application/captive+json The server then responds with the JSON content for that client: Pauly & Thakore Expires September 12, 2019 [Page 5] Internet-Draft Captive Portal API March 2019 HTTP/1.1 200 OK Cache-Control: private Date: Mon, 04 Dec 2013 05:07:35 GMT Content-Type: application/captive+json { "captive": true, "user-portal-url": "https://example.org/portal.html", "vendor-info-url": "https://flight.example.com/entertainment", "expire-date": "2014-01-01T23:28:56.782Z" } Upon receiving this information the client will provide this information to the user so that they may navigate the web portal (as specified by the user-portal-url value) to enable access to the external network. Once the user satisfies the requirements for extenal network access, the client SHOULD query the API server again to verify that it is no longer captive. 5. Security Considerations TBD: Provide complete security requirements and analysis. 5.1. 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 unencrypted sessions. 6. IANA Considerations 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 5 Pauly & Thakore Expires September 12, 2019 [Page 6] Internet-Draft Captive Portal API March 2019 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 7. 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. 8. References 8.1. Normative References [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/RFC2818, May 2000, . [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002, . [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, . Pauly & Thakore Expires September 12, 2019 [Page 7] Internet-Draft Captive Portal API March 2019 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known Uniform Resource Identifiers (URIs)", RFC 5785, DOI 10.17487/RFC5785, April 2010, . [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, "Network Time Protocol Version 4: Protocol and Algorithms Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, . [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, DOI 10.17487/RFC6066, January 2011, . [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, . [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014, . 8.2. Informative References [I-D.ietf-capport-architecture] Larose, K. and D. Dolson, "CAPPORT Architecture", draft- ietf-capport-architecture-03 (work in progress), December 2018. Authors' Addresses Tommy Pauly (editor) Apple Inc. One Apple Park Way Cupertino, California 95014 United States of America Email: tpauly@apple.com Pauly & Thakore Expires September 12, 2019 [Page 8] Internet-Draft Captive Portal API March 2019 Darshak Thakore (editor) CableLabs 858 Coal Creek Circle Louisville, CO 80027 United States of America Email: d.thakore@cablelabs.com Pauly & Thakore Expires September 12, 2019 [Page 9]