[SOLVED] How does SSH and github determines the user name?

How does SSH and github determines the user name?

I created two SSH keys: ~/.ssh/id_ed25519 and ~/.ssh/dr_dror_id_ed25519. I also uploaded their public parts to two different GH account (personal and work, respectively). Next, I also added the following ~/.ssh/config:

Host drorata-personal
  Hostname github.com
  User git
  IdentityFile ~/.ssh/id_ed25519

Host dr-dror
  Hostname github.com
  User git
  IdentityFile ~/.ssh/dr_dror_id_ed25519

Now, whether I try:

ssh -T git@drorata-personal

ssh -T git@dr-dror

I get the same response:

Hi drorata! You've successfully authenticated, but GitHub does not provide shell access.

Where does drorata come from? I am guessing it's the username I have in my private account. What am I missing?

Solution

I suspect this is ssh-agent trying all the identities that have already been added; IdentityFile would just specify any that need to be added for that specific Host match. You should be able to confirm this with ssh -Tv git@dr-dror, which will give the verbose output of the connection attempt (including, but not limited to, the specific key used to authenticate).

If my suspicion is correct, then you can add IdentitiesOnly yes to each stanza to have the agent use only the specified key(s) for the Host match. Once that's done, both ssh -T commands should return the correct username.