Backend Developer for Sign-up/Log-in and Payment System

FXive ([login to view URL]) is a real-time sound effect synthesis framework in the browser developed at Queen Mary University of London. It is currently front-end only. We'd like to subcontract a backend developer to implement: - Sign-up and login functionality, saving user data safely. - Subscription - Any subscribed user would pay a monthly fee. The subscribers can use the website freely and download as many sounds as they can without limitation. The subscription should be able to be cancelled any time. Payment system: - Simple version: Any visitor or user should be able to create sounds, then if they want to download them, they would pay a small fee directly. The logged-in up users with credit card information, should be able to do this fast without re-typing the card information. Alternatively, paypal gateway could be used for this as well. The subscribed users should be able to directly download the sounds, after they create them. - More complex version: The users who are logged-in can add the sounds to a basket and then, if they like, they can go to another model and add more sounds to their basket. While adding to their basket, then can give short names to the sounds, so they can remember before purchase. At the end, they can go to their basket and download the sounds according to how many items they want to get. (Not a requirement, but discussable) User presets: Subscribed users would be able to save custom presets and then would be able access the preset they created, whenever they visit the website again. Ps. The budget is open to discussion