Hell, I can do _all_ my work as somebody else with "git config user.name" and "git config user.email".
If that's really a genuine concern, then a) you are working with a big bag of dicks and b) there are _way_ worse things that person can do with write access to the repository than masquerade as somebody else.
If that's really a genuine concern, then a) you are working with a big bag of dicks and b) there are _way_ worse things that person can do with write access to the repository than masquerade as somebody else.