How do I use GitHub through harsh proxies?

Question

Given the following constraints, how can I use GitHub from Windows and Unix?

• All access to the internet is restricted to a proxy
• The proxy only allows

Answer 1

[Since my addition to the first answer given above did not get approved within four days, I put it here.]

Note that corkscrew and connect, as well as the standard Unix command nc only support basic authentication (which insecurely transmits the password).
tunnel-auth version 0.04 in addition supports digest authentication.

In case your proxy requires NTLM authentication, all these commands may be combined very nicely with cntlm as follows:

Choose a local port (e.g, 8080 as in the examples below) on which cntlm will listen (performing the user authentication with the proxy and forwarding any further packages to/from the proxy), set the port etc. (e.g., in /etc/cntlm.conf), and use instead of the ProxyCommand given above (with the respective port number inserted):

ProxyCommand corkscrew 127.0.0.1 8080 %h %p

or

ProxyCommand connect -H 127.0.0.1:8080 %h %p

or

ProxyCommand nc -X connect -x 127.0.0.1:8080 %h %p

or

ProxyCommand tunnel-auth -p 127.0.0.1:8080 -r %h:%p