I'm trying to restrict some areas of my site to paying members. Is there any free open-source scripts for this? osCommerce is basically a shopping cart, but it's not exactly what I am looking for, unless there is a way to modify it to be able to restrict access, send invoices, display billing info, and so on.
If there is no such script then could someone point me in the right direction, to tutorials on online payments, secure connections and so on. I know how to handle php and mysql fairly well, I just never came across online payments.