cafe wifi with freeradius

[Muhammed Buvaydani]

Hello
I working on freeradius management system and I wish to install it into cafe .
my system contain self registiration so user can register for new account and password will send through sms .
my question is how can I prevent another users from using my system ie . I want only cafe clients to use my system .
so if user is inside my cafe and has table he can Access internet by register new account .
how can I do this ? how can I prevent non client user from Access login page .
I have idea like putting  QR code onto every table inside my cafe and if user want to acccess internet he must read this code by his phone and he will redirect to register page to has new account , but I don't know how to implement this idea
Are thgere any idea or way to make this