Openhab & RFID-readers

Hi All,

Couldn’t find a direct answer to my problems in many threads, therefor asking it here:
I want to setup an access-control module with several badges. Mostly it’s for locating who is where, and count perhaps the number of people in a room.
Which readers can I use, icw which biding?

Is there any relevant info on setting this up? I don’t want to use 3rd party-apps or software, simply get the results of rfid-readings into openhab.
Don’t quite know where to begin.

Many thanks!