networking - what ports to open up for GitHub to install and work?

I want to use GitHub on a server where user accounts are not supposed to be able to go online otherwise. The GitHub Windows app does not even install without users' downloading it themselves (see my previous question), but also for my regular use, what is the bare minimum one needs to open up?

By opening up I mean user account privileges (under Windows Server 2012 specifically) or firewall rules.

See also the follow-up on StackOverflow about whether an open port 9418 is all I need.

Thanks!