When printer/job requires authentication, for example SMB share, it is not possible to authenticate the job. The plan is to implement additional action to authenticate the job.
User should be notified about the authentication required.
There are several bugs in the printer queue, for example it is not refreshing correctly. Code is quite old (2010), model polls for changes using IPP protocol. Newer method is to listen to DBus service. The same service can be used to implement notifications.

Some additional refactoring might be required.