TOR onion routing basics

[KissT]

I'm looking for a tutorial to achieve the following simple TOR routing:

 - Clients behind the OPNsense router, can access ".onion" addresses.

That is it, I don't want to:
 - Route any other traffic across TOR
 - Run an exit point for TOR
 - Do other magic

I realize that "simple" is relative, and it will need policy based routeing, DNS rewrite, and etc etc, but if anyone set up OPNsense like this before a short tutorial would be excellent.

[fabian]

You have to use the Tor DNS resolver for Tor and you have to setup the mapped ip pool for transparent proxying.