I wish I did understand. I've read the docs for 1.5 (the version bundled with Ubuntu 12.04). And yet I don't see any mention of creating a user or specifying what user CUPS processes will run as. I did see settings for authentication types to use the host UNIX users, but the system still doesn't seem to be able to handle comparing the incoming web credentials to the system and continue to the admin web pages...

I think this may be more of an issue with something about Ubuntu's setup of CUPS than CUPS internal? Is there not a complete step-by-step guide for Ubuntu 12 installation of CUPS?