Two way communication through a HTTP proxy

Question

I'm trying to come up with the most appropriate way to make a two way socket connection through a HTTP proxy - lets say it's a telnet style protocol. Unfortunately I also need to support NTLM authentication (with the proxy) as well as Basic and Digest, in addition to any other future authentication mechanisms that I can't forecast.

If it was just basic and digest I'd handle the connection myself, but I really don't want to get stuck in the mire that is NTLM. Looking at the underlying AuthenticationManager API it looks very tied to HttpWebRequest so I can't leverage that functionality if I'm using a socket/tcpclient/whatever or even writing a new WebRequest derivation.

Playing around with HttpWebResponse yields a stream that can't be written, using the RequestStream after the response stream has been retrieved gives a concurrent io exception.

Having run through all the possibilities I can think of, I've come up with some nasty code that gets out the NetworkStream associated with a HttpWebRequest which allows two way communication:

  .....
  HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
  Stream str = resp.GetResponseStream();

  System.Type type = str.GetType();
  PropertyInfo info = type.GetProperty("Connection", BindingFlags.NonPublic|BindingFlags.Instance| BindingFlags.Public);
  object obj = info.GetValue(str, null);
  type = obj.GetType();
  info = type.GetProperty("NetworkStream", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);
  object obj2 = info.GetValue(obj, null);
  NetworkStream networkStream = obj2 as NetworkStream;

Which I'm fairly repulsed by (it won't work with Mono for a start), so I'm wondering if there's a better way using public APIs which will allow me to leverage the built in runtime functionality of proxy authentication.