I've had a vbulletin forum already, and will develop another app.
I don't want new login system on on the new app, the best idea is just to use existing vbulletin login. My new app just need to check if a user has logged into vbulletin, if not, send him to vbulletin login page, otherwise, let him go further to use my app showing his vbulletin username. It looks quite simple. But I have no clue to begin, any one could help me a little bit? Many thanks in advance.