How let Google bots to see restricted areas to members ?

I have some contents at my forum that are restricted to members only, if visitors can't see those contents so neither Google bots.

Is there something I can do to allow that safely ?

Tks

Unfortunately no ,

There are some hacks out there but what you request is called cloaking and if SE's will discover you are cloaking they will remove your site from index.

That's a good point Mert, SE's may consider this as cloaking.