Facebook Registration JSON

I would like to implement the Facebook Registration tool into my website. This will replace the existing sign-up method. The facebook registration tool can be found here <[login to view URL]>. I will be using the JSON string as I would like to add fields that will give me information not present on facebook. I currently have the form I need and the return URL entered, however when it returns the signed_request array is empty. My knowledge of this is fairly good, but not enough to get it working. All I need is for somebody to use the example code from facebook working and return data such as "name" into a $variable ready for insertion into my database.