I followed the accepted answer of How do I hide a particular user from the login screen? (the one about modifying /var/lib/AccountsService/users/USERNAME) to hide the user guest-config from my lightdm login screen.
This works fine and the account vanished from the user list after a reboot.
However, now I need a way to log into that account anyway. On Windows (at least back on good old Windows XP), I could press Ctrl+Alt+Del twice on the login screen to get an old-school login mask prompting me to type the username and password manually. This does not work on Ubuntu.
How can I get a similar graphical login mask where I must enter the username manually? I don't want to lose the normal user list for all other visible accounts though. Just add this to log into invisible accounts.
System is Ubuntu 16.04 with Unity Desktop.
