Get current used certificate (id?) by IP or Mac

Hi all, I want to write a web interface. The web interface is available behind an WPA2 eap-tls network(using freeradius). And when the user logging in with their username & password, it should check if the user logged in to the WPA2 Network, with an specific Username. So for example is there a possibility to activate a mysql/psql/.. database and write into a table all current users which are logged in or is there a possibility to check with an SH-command the current users or an user by ip/mac/.. or etc. . ? Thanks for any response ;) MfG. Max