Shouldn't be needed, no. The client presents the private key, the server will automatically find the corresponding public key (or complain that it can't).
Exactly.
It should be Identity file (private key - not public key)
One thing, missing is the passphrase of the identity file.
I had conversation with Akshay regarding it.
We were agree to change the label for password to Password/Pass Phrase and the certificate to 'Identity File'.
So - the same textbox can be used to take password. And, pass-phrase in case of identity file is provided.
And - add a label to show tip about the Password/Pass-phrase at the bottom of the dialog to explain that use of the text-box.
That may not be necessary - but I guess the fields should be re-ordered so the password/passphrase box is at the bottom. It would be more of a logical flow that way.