git setup for multiple repos on same server

Probably a simple question, but I am at a loss here...

In github one can add a deployment key for each repository which only gives access to that single repository.

But for one client I have two projects managed with git on the same server (project A and project B). If I use the public key for project A, github tells me I cant use it as a deployment key for project B and vice versa.

How can I create another public key and setup git to use one key for project A and the other one for project B?