Custom auditing

Hi,

I'm trying to create a POC regarding auditing. The concept is a logon-trigger which allows or disallows your session to logon (based on some criteria). One of the requirements is that a custom made error message (raised through raise_application_error) should be logged somewhere.

I'm wondering whether it's possible to log this in the AUD$, column returncode?
I've found a lot of info about creating your custom-made error message and a lot of info about auditing, but not how to combine the two.

Is this even possible or should we write some custom logging?

Thanks a lot for all your feedback.