[TYPO3] Typo3 - VB bridge - login fe_user from another application

[Jan Slusarczyk]

Hi,
I'm struggling to bridge a forum (vbulletin) and Typo3.

vbulletin_connect extension lets me authenticate fe_user against forum 
user list and starts both typo3 and forum sessions perfectly. Users 
logging on Typo3 pages are authenticated in both places.

Now I need to have it working the other way around. I need to start 
Typo3 session for people who log on on forum first, so that when they 
browse to typo3 pages they will be automatically recognized.

What is the best strategy for starting typo3 session "externally"? Will 
it be enough to set fe_typo_user cookie? How to keep them logged on?

Any hints will be very appreciated.
Cheers
Jan