WiFi Access w/Password

How do I control access to my WiFi network(s)? I have several public locations and would like to sell access to the general public (like a mini T-Mobile HotSpots).

The goal is to have a customer with a user name and password open thier wireless device and be directed to a log in website. Once they are logged in, they would be free to use the WiFi internet for the duration of that login (while they are logged in at that location).