A full SSH like pipe protocol is likely overkill. We could consider adding a command line option for the case when credentials are provided, which: 1) Hides the "interactive" parts of the login GUI, so that only the "login progress" part is visible. Or, create an entirely new login progress GUI. 2) Upon errors, after clicking OK in the error dialog, the client should exit rather than return to the login GUI.
I think this is a duplicate of bug #4678
*** This bug has been marked as a duplicate of bug 4678 ***