MessageHook is called after a message from Fidelio has been
unpacked into a hash and before the record is passed to handle_message().
It can be used to change or transform any fields in the record before it
is passed to handle_message() and processed by Auth- FIDELIO. The first
argument is a pointer to the AuthBy FIDELIO clause, and the second is a
pointer to a hash containing the unpacked record fields.