How to add and run a python script before the user can login

[ryanls27]

Hello everyone.
I'm still learning new stuff with vpn and I'm struggling on how I can run a python script that checks the operating system of the user before connecting.
Upon researching, I've encountered the term management interface but I can still grasp the general thought for this one.

I will apologize in advance to everyone but I really do need your help.
Thanks.