This is the re-creation of an old idea:
Some applications/systems use naming schema different then simple username. Good example might be FUDO running in "bastion" mode. In that case username consists of two parts and looks like:
which of course is not correct from NAAF point of view and results in "User not found". Simply cutting the part from the "#" would do the trick.
So there is a need for a recipe for getting the username from the given input data.
New attribute of user repository defining additional username format(s), eg. with regexp: ([^#]+)#.* in this case, or something similar would solve the problem quickly and elegantly.
this is a real life problem. It applies to an environment of about 8,000 NAAF users.