| Internet Engineering Task Force | A. Hutton |
| Internet-Draft | Unify |
| Intended status: Standards Track | J. Uberti |
| Expires: February 19, 2015 | |
| M. Thomson | |
| Mozilla | |
| August 18, 2014 |
This specification allows HTTP CONNECT requests to indicate what protocol will be used within the tunnel once established, using the Tunnel-Protocol request header field.¶
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The HTTP CONNECT method (Section 4.3.6 of [RFC7231]) requests that the recipient establish a tunnel to the identified origin server 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 HTTP Tunnel-Protocol header field identifies the protocol that will be spoken within the tunnel, using the application layer next protocol identifier [RFC7301] specified for TLS [RFC5246]".¶
When CONNECT is used to establish a TLS tunnel, the Tunnel-Protocol header field may be used to carry the same next protocol label as was carried within the TLS handshake. However, the HTTP-Protocol is an indication rather a negotiation since HTTP proxies do not implement the tunneled protocol.¶
Clients include the Tunnel-Protocol Request Header field in a HTTP Connect request to indicate the application layer protocol used within the tunnel.¶
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-id¶
protocol-id = token ; percent-encoded ALPN protocol identifier¶
ALPN protocol names are octet sequences with no additional constraints on format. Octets not allowed in tokens ([RFC7230], Section 3.2.6) must be percent-encoded as per Section 2.1 of [RFC3986]. Consequently, the octet representing the percent character "%" (hex 25) must be percent-encoded as well.¶
In order to have precisely one way to represent any ALPN protocol name, the following additional constraints apply: ¶
With these constraints, recipients can apply simple string comparison to match protocol identifiers.¶
For example:¶
␉␉ CONNECT turn_server.example.com:5349 HTTP/1.1 ␉␉ Host: turn_server.example.com:5349 ␉␉ Tunnel-Protocol: turn ␉␉
To Be Added¶
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.¶