Hi, basically they redirect "you" (as a client) from client's page to their own servers and there run all relevant stuff, like authorization, for instance. Don'

Hi, basically they redirect "you" (as a client) from client's page to their own servers and there run all relevant stuff, like authorization, for instance. Don't forget they monitor all your(client's) actions and keep the history. If something abnormal happens the Hollywood principle begins to work. However, I think you wanna see PayPall API first. Cheers, Oleg.