I have set up printer sharing on a (local) headless ubuntu server running cups.
My Question: Is there a way to add authentication (like username and password) to the shared printer, so only authenticated clients can use it and print with it?
See /etc/cups/printers.conf
and add
AuthInfoRequired username,password
to the printer segment of your printer (each printer that requires this needs 1 line) with the username and password you require. You need to stop cups before and start it after doing this.