I'm updading my authentication plugin to work with osTicket v1.17 and, in my case, the usedname is an UUID (for example "f483dd48-0597-4a97-890d-605af33b964e") but this username does not seem to arrive to the authentication plugin. I've tested with "f483dd48-0597-4a97-890d" and it arrives, so I think there is a limitation at some point in the osTicket source code.
Thanks in advance.