Recently, after reinstalling POP_OS on my System 76 laptop I was having problems connecting to my HP LaserJet MFP M227fdw. POP_OS is a Ubuntu derivative especially designed for System 76 hardware and my setup is based on Ubuntu 19.04.
The Gnome Print manager was not finding the printer and when I tried to install the network print, which it would, my username and password would not authenticate. Simply put, this is a security feature, but on a home based single user system I needed to safely bypass.
The procedure is pretty simple. First, I needed to add myself to the lpadmin group (you will probably need to enter your sudo password):
sudo usermod -aG lpadmin <username>
Last thing is to restart CUPs. This can be done by typing:
sudo /etc/init.d/cups restart
Then go to the CUPS web interface at
http://localhost:631/ and freely add your printer. It worked for me flawlessly and I hope it helps you as well.