How does this Facebook widget work?

Brad, I've seen several sites that might be using that WordPress plugin you mentioned. What's the name of that plugin, btw?

Log in with Facebook works as follows.

1) The site viewer clicks the log in with FB button.
2) This triggers site code to send a request to Facebook via there API
3) Facebook responds with a permission dialog for the user to approve (approve the app)
4) If the user approves Facebook then responds to the site code with a Token (a long string of unique characters)
5) The site code then uses this Token to request the info it needs, this is called a signed request, as the request for the info is 'signed' with the Token it got in step 4
6) The site code then takes the info it got from Facebook such as name ,email etc. and then saves it to the database as if the user had filled it out in the sites signup form.
7) The site code then logs in the user with this account it created automatically for the user in step 6

You just created an account for someone and logged them in with Facebook.

How do I know how this works?
I have written over 150 Facebook apps, and over 1 million lines of Facebook integrated code.

Brett

PS) If all this seems confusing it should cost around $50 for this to be done for you on a freelance site, its generally a one hour or less job for someone who knows what there doing. I know this as well because I have done it on freelance sites scores of times for people.