Simple Security System for Auth Users to login to URL

Hi all,

Im searching for a system that will give me the option to give my users to login to URL based on their IP and other security methods.

Im searching for a light and simple system that will give me also the option to add users
Also i need an Registration Form for new users that have the ability to pay with paypal (in the same form), and after they pay, they get a new user and they get the ability to login into the URL.

Tried to find but without success