"Unauthorized" error when adding printers through CUPS using Google Chrome in Ubuntu 18.04 LTS

Update 2019-01-09: I have found that CUPS 2.2.8 works without a problem with Google Chrome in Ubuntu 18.04. I downloaded and installed it from https://launchpad.net/ubuntu/+source/cups/2.2.8-5ubuntu1.2

Please note that the bug for CUPS 2.2.7 is filed at: https://bugs.launchpad.net/ubuntu/+source/cups/+bug/1769893

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CUPS 2.2.8 installation steps

Run all the following from a terminal window.

Install the prerequisites:

sudo apt install autoconf build-essential libavahi-client-dev \
    libgnutls28-dev libkrb5-dev libnss-mdns libpam-dev \
    libsystemd-dev libusb-1.0-0-dev zlib1g-dev

Download CUPS 2.2.8 and extract it and enter the new directory created:

cd /tmp
wget -c https://launchpad.net/ubuntu/+archive/primary/+sourcefiles/cups/2.2.8-5ubuntu1.2/cups_2.2.8.orig.tar.gz
tar zxvf cups_2.2.8.orig.tar.gz
cd cups-2.2.8

Run the configure, make and make install:

./configure
make
sudo make install

You might want to put a hold on CUPS so it doesn't update back to 2.2.7 which still has the issue with unauthorized:

sudo apt-mark hold cups

Then all you should have to do is restart the cups.service:

systemctl restart cups.service

Check if the service is running:

systemctl status cups.service

If CUPS fails to restart, reinstall the daemon then restart the service again:

sudo apt install --reinstall cups-daemon
systemctl restart cups.service

Then access in Google Chrome http://localhost:631

The CUPS homepage might show 2.2.7 still, but try clicking on Administration and it should show 2.2.8.

Hope this helps!