> Type in a github username Exactly. That would be the deliberate steps I mentioned as a gate for this causing a problem. If you give it someone else's key you

> Type in a github username Exactly. That would be the deliberate steps I mentioned as a gate for this causing a problem. If you give it someone else's key you have a problem, though a minor one unless you've been conned into doing so by an adversary who will later scan for accounts that allow their key pair for auth. Importing your own public key this way is not problematical at all. Of course you might end up with people publishing their private key along with the private one, by error or because it seems convenient & they don't think things through...