[otrs] PHP as login interface

Hi all, I have a question concerning the possibility to integrate OTRS in an already existing PHP web frontend. We have a customer backend and i'm eager to use otrs as our ticket support system. Of course the backend has it's own authorisation system (based on php sessions). My questions is if it is possible to have otrs use the data of the php session. As i rather don't have the situation in which my clients have to use a seperate login for the ticket system. Has anyone has tried this before? Or are there some guidelines anyone can give in making the authorisation module for otrs myself? Thanks in advance, Maarten