I need to add a facebook signup function on my existing website, so people have to choice to either register via the normal sign up available on my website ("[url removed, login to view]") or by clicking on the "Sign up with Facebook" button.
When clicking on "Sign up with facebook" button, a JS window would popup (jQuery, perhaps), and they would be able to signup with facebook, and the fields would look similar to this "[url removed, login to view]"
When registered, its like the [url removed, login to view] page, entries are inserted in the Db, and they get automatically login.
We have to add some error handligns, such as 3 characters minimum and 15 chars max for the username, no username duplicates, alpha numeric only
Most info about everything we need / personalization etc. should be there : [url removed, login to view]
The 'Sign up with Facebook' button should be easy for me to add to any page on the website, by adding a few lines of code to the pages. So a class would probably be needed.
I would like to have this feature done quickly and efficiently.
You should also offer a guarantee for a few months so that if the feature stops working because Facebook changed something on their side, we need to adapt to it, if it's not too big of a change.