[julianlam]

Is it not possible to restrict access to the git server from a VPN server only?

Just off the top of my head, that's one thing you can do.

[mlyle]

Yah, that's a "closed org". When you need to deal with the public at large, you need to deal with user registration issues and spam.

[Dobbs]

So now every person who wants to contribute to your open source project has to setup a VPN client?

The parent comment was explicitly about non-closed (e.g. private) orgs.