Users submitting AirPrint jobs to non-secure printers are logged as Guest users in the iPrint server audit log. This is because non-secure printers do not require user credentials to print.
If a user is not authorized to use a secure printer, the printer does not print because of an authentication failure. The iOS device does not display any message to indicate the authentication failure.
Users might be prompted for credentials for non-secure AirPrint printers.
Secure printing to iPrint printers through AirPrint is supported only on iOS 6.x and later versions.
“The printer is no longer available” message is displayed even if the printer is working fine.
If you print to a secure AirPrint printer by providing your credentials, the credentials are stored, and you are not prompted for the credentials when you print to that printer in the future. This is the default behavior of AirPrint.
Whenever a user prints to a secure printer, an "invalid request-URI" message is displayed in the Apache error logs.