To add "Basic" proxy support is simple - you initially send:
CONNECT 203.202.137.58:443 HTTP/1.1Not all proxies allow Basic authentication - eg ISA may insist on NTLM.
Host: 203.202.137.58:443
Proxy-Authorization: Basic b2NlYW5pYVxkYWx0b25wMjpQYXNzd29yZDE=
Does anyone know an implementation of NTLM at this level (ie NOT using WebRequest)
Wal

SSL Tunnel through ISA
FlorinB
I am not aware of an implementation of NTLM at that level,
but when the proxy requires the NTLM auth it sends the challenge,
so you could possibly use SSPI on the client side to do the magic.
What exactly does the proxy send in case of NTLM
Vidhya
What it sends is not documented by Microsoft. It has been documented by others but only by oberservation. I *could* implement NTLM in c# from the java or curl implementations but it would seem a waste in that I'm programming in Windows to start with! (its also not a 5minute job). I would have thought there was at least one other person who had to run a windows app. through a proxy firewall that requires NTLM authentication...