rewrite login/registration functionality of website

I need someone to rewrite the login/registration aspect of my website. Users can login or register directly through the site and also using Facebook connect. You need to handle front end and backend validation as well as the scenarios when a user may have initially logged in via facebook without creating an account, but then returns to create an account (so both accounts need to be joined into 1). We need to provide the ability for a user to connect and disconnect their account from facebook. This needs to be fully cross browser tested. I require well written, commented code that follows latest security considerations. I will provide you very detailed requirements as well as a detailed list of testing scenarios with an 'action' and 'expected outcome' for each scenario. Please only apply for this job if you have worked with facebook connect before. This project has started twice and twice been aborted so I'm looking for someone that knows what they're doing. Also I'm looking for this to be fully completed in 2-3 weeks. I will be available to answer any questions as we go and will provide a test server.