Could someone advise me, guide me?

I'd like one of my forums is accessible only to certain users : with a call to the forum from another application.

I think I read that YAF could exploit IDs from another application (my English is quite poor :? ). It would identify the user. Good !

I think using an url access token to go directly to this reserved forum but... how to hide this forum to the other users ?

Thank you in advance for your help