WiFi MAC auth radius server

Hi

Let me explain what i am trying to achieve.

I have a number of Draytek 2862Ln model firewall routers in various shops up and down the country. I want to configure a guest wifi on all those routers. the Draytek Routers has an option for "captive portal" and "MAC authentication". The idea is if a customer goes to 1st shop and connects to the guest wifi on the draytek they will see a splash screen asking them to login using facebook or google and then they will have internet access.

If they then went to another shop they would simply connect to the guest wifi and have internet access they would not need to enter their facebook or google details again as their MAC address of their wireless client will have been captured by the radius server on a database when they previously connected at the other shop.

I have serched for various MAC auth radius servers but i cant seem to find one that will do what i want. I am looking for a open source free radius server, i have looked at "packetfence" "wifi dog" and "Zeroshell" but they dont seem to do what i have explained.

I have attached screenshots of the Draytek Web GUI. CAn anyone advise what free server is out that that will allow me to achieve what i have explained.

Thanks in advance.

Hiran