HTTP Connect - Tunnel Protocol For WebRTC
draft-hutton-httpbis-connect-protocol-00

Abstract

This document describes a mechanism to enable HTTP Clients to provide an indication within a HTTP Connect request as to which protocol will be used within the tunnel established to the Server identified by the target resource. The tunneled protocol is declared using the Tunnel-Protocol HTTP Request header field. Label usage relating to the use of HTTP Connect by WebRTC clients (e.g. turn, webrtc) are described in this document.

Status of This Memo

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This Internet-Draft will expire on December 29, 2014.

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Use Cases
• 3. The Tunnel-Protocol HTTP Request Header Field
• 3.1. Header Field Values
• 3.2. Syntax
• 3.3. TURN as the Tunnel Protocol
• 3.4. ICE-TCP / WebRTC as the Tunnel Protocol
• 4. IANA Considerations
• 5. Security Considerations
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Authors' Addresses

1. Introduction

The HTTP Connect method (Section 4.3.6 of [RFC7231]) requests that the recipient establish a tunnel to the destination origin server identified by the request-target and thereafter forward packets, in both directions, until the tunnel is closed. Such tunnels are commonly used to create end-to-end virtual connections, through one or more proxies, which may then be secured using TLS (Transport Layer Security, [RFC5246]).

The RTCWEB use cases and requirements document [I-D.ietf-rtcweb-use-cases-and-requirements] includes a requirement that a WebRTC Client must be able to send streams and data to a peer in the presence of Firewalls that only allow traffic via a HTTP Proxy, when Firewall policy allows WebRTC traffic. To facilitate this and to allow such a HTTP Proxy to be provided with an indication that WebRTC related real-time media is to be included in the tunnel this specification defines the Tunnel-Protocol Request header field and associated labels. This allows the proxy to identify the protocol being used in the tunnel as early as possible therefore enabling the proxy to make informed policy decisions. The type of policy decisions the proxy may make is not specified here but may include rejecting the request with a HTTP status code responses or prioritizing connections. As described in Section 4.3.6 of [RFC7231] and 2xx response indicates consent for the client to switch to tunnel mode.

The HTTP Tunnel-Protocol header field may be used in conjunction with and complements the application layer next protocol extension [I-D.ietf-tls-applayerprotoneg] specified for TLS [RFC5246]". In the scenario where the HTTP Connect is used to establish a TLS tunnel then the HTTP Tunnel-Protocol may be used to carry the same next protocol label as carried within the TLS handshake. However, the Tunnel-Protocol is an indication rather a negotiation since the HTTP Proxy does not implement the tunneled protocol. ALPN Labels are already defined for TURN in [I-D.patil-tram-alpn] and WebRTC [I-D.thomson-rtcweb-alpn] and are re-used here.

1.1. Requirements Language

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 RFC 2119 [RFC2119].

2. Use Cases

The following two use cases are considered:

• The WebRTC Client issues a HTTP CONNECT request to the HTTP proxy with the TURN server address in the Request URI.
• The WebRTC Client issues a HTTP CONNECT request to the HTTP proxy with the TCP address of a WebRTC peer in the Request URI. This is used in the case of establishing ICE-TCP [RFC6544] with a WebRTC Peer.

3. The Tunnel-Protocol HTTP Request Header Field

The client MAY include the Tunnel-Protocol Request Header field in a HTTP Connect request to indicate the application layer protocol within the tunnel.

3.1. Header Field Values

Valid values for the protocol field are taken from the registry established in [I-D.ietf-tls-applayerprotoneg]. For the purposes of WebRTC, the values "webrtc" [I-D.thomson-rtcweb-alpn] and "turn" [I-D.patil-tram-alpn] are applicable.

3.2. Syntax

The ABNF (Augmented Backus-Naur Form) syntax for the Tunnel-Protocol header field is given below. It is based on the Generic Grammar defined in Section 2 of [RFC7230].

Tunnel-Protocol = "Tunnel-Protocol":" protocol | protocol-extension

protocol = "webrtc" | "turn"

protocol-extension = token

3.3. TURN as the Tunnel Protocol

The RTCWEB transports specification [I-D.ietf-rtcweb-transports] requires that a WebRTC client support the modes of TURN that uses TCP and TLS between the client and the TURN server in order to deal with firewalls blocking UDP traffic. In the case where HTTP Connect is used to establish a tunnel to the TURN server the client SHOULD include the "Tunnel-Protocol" header field with the value "turn" [I-D.patil-tram-alpn] as shown in the example below.

		 CONNECT turn_server.example.com:5349 HTTP/1.1
		 Host: turn_server.example.com:5349
		 Tunnel-Protocol: turn
		

3.4. ICE-TCP / WebRTC as the Tunnel Protocol

[I-D.ietf-rtcweb-transports] also requires that a WebRTC client support ICE-TCP [RFC6544] as a mechanism to allow webrtc applications to communicate to peers with public IP addresses across UDP-blocking firewalls without using a TURN server. In this case the client SHOULD include the "Tunnel-Protocol" header field with the value "webrtc" [I-D.thomson-rtcweb-alpn] as shown in the example below.

	     CONNECT 198.51.100.0:8999 HTTP/1.1
	     Host: 198.51.100.0:8999
	     Tunnel-Protocol: webrtc
		

Note: The protocol "c_webrtc" described in [I-D.thomson-rtcweb-alpn] is not relevent in this context and when used at the TLS layer the client SHOULD use "webrtc" in the Tunnel-Protocol header. OPEN ISSUE - Is this correct?

4. IANA Considerations

To Be Added

5. Security Considerations

In case of using HTTP CONNECT to a TURN server the security consideration of [RFC7231], Section-4.3.6] apply. It states that there "are significant risks in establishing a tunnel to arbitrary servers, particularly when the destination is a well-known or reserved TCP port that is not intended for Web traffic. Proxies that support CONNECT SHOULD restrict its use to a limited set of known ports or a configurable whitelist of safe request targets."

The Tunnel-Protocol request header field described in this document is an optional header and HTTP Proxies may of course not support the header and therefore ignore it. If the header is not present or ignored then the proxy has no explicit indication as to the purpose of the tunnel on which to provide consent, this is the generic case that exists without the Tunnel-Protocol header.

6. References

6.1. Normative References

6.2. Informative References

Authors' Addresses