[click170]

You don't have to rely on Github, you can use Github Enterprise which gives you a little bit more control and allows you to run it on your own servers.

That said, my understanding is that authentication even for Github Enterprise is done through Github itself. (Someone please correct me if I'm wrong)

[sitharus]

Authentication for Github Enterprise is customisable. At my organisation we use LDAP, but it has built-in auth and a few others IIRC.

The enterprise product is stand-alone, it doesn't talk to the cloud version.