I would like to restrict access to a file until the user has paid for it. This is easy enough if I served the file via a web app, but it seems more efficient to have httpd serve the file. Is there a way to get apache to ask a web app if it can serve a file before serving it? As I'm typing this it seems like it should be trivial but I'm not coming up with a good answer via google. Thanks in advance for any help.