So, I started working on Linux and one of my first tasks has been to learn to use git, the open source version control system used by, among others, Linus Torvalds. I'm familiar with a number of SCM systems but git has quite a lot of new stuff for me. I also installed gitosis for added security. Gitosis removes the need to create user accounts for everyone who needs to read or write to the repository, which improves security a lot. Setting it up had it's small quirks which meant I couldn't use the otherwise excellent guides to the point. But I did get there eventually.
Anyways, what I wanted to do was to check that the user is who he says. By simply saying "git config firstname.lastname@example.org && git config user.name=Mr. Fake" a user can hide his identity - in practice allowing him to add what he wants to the repository as long as he has write access. Also, there is no extra security for anything else. For instance if you have conditional hooks in your git repository, you can't just the user id for access rights.
The solution is to use gitosis and check that the user really is who he says he is. I already asked this question in stackoverflow and then ended up solving the problem myself. The solution requires fixing gitosis, reinstalling it and the adding a pre-receive hook to the git repository. Not overly complicated, but hopefully someone could add that fix to the "official" gitosis code as well.
This solution verifies that the user email address used to create the ssh key for gitosis matches the address the user is using which should be pretty secure. This way the repository history is correct and the culprits can always be tracked down.