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
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 12, 2019.
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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.
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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"
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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
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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:
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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
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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,
<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>.
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[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>.
[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,
<https://www.rfc-editor.org/info/rfc5905>.
[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>.
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
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Darshak Thakore (editor)
CableLabs
858 Coal Creek Circle
Louisville, CO 80027
United States of America
Email: d.thakore@cablelabs.com
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