CNAM Customer Web Site

I'm looking to clone [login to view URL] But not an exact duplicate. You can change the look and feel of the site as long as it provides the same functionality. As you can see it's a simple site, but requires customers to sign-up for service before use. They must put a credit (paypal) in their account before use. As the customer uses the service, their account is debited towards zero and the then service is disabled. When they sign-up and confirm their email, an email is sent with their unique key is sent to them. This key must be generated of the fly. This key is use with the look-up request to track which customer is making the the request and debit their account. For the customer to use the service, they direct their requests towards my web site, validate the key, act as an proxy to make the query towards the CNAM Server, parse the results for the required information, and then debit their account returning the info in a usable form. I need to make sure the customer can not discover the method to bypass my web site and make queries without my knowledge and/or bypassing fees. Thanks, Bart