Comment 54 for bug 1849859

This bug seems to still be active in Ubuntu 20.4
The "AuthInfoRequired username,password" workarround did NOT work on my system, as when I restarted cups, it rewrote the printers.conf file without the password and user.

However what did work for me was adding the printer and adding my credentials at the same time in the SMB printer box! The format that worked was username:password@host_computer/printername. In the dialog, it deletes the username and password on the smb: line but adds them in the password and username boxes and this time writes them in the file.

This seems very strange to me but it works for me!