在没有明显重定向的情况下将Facebook登录添加到站点的最佳方式

Question

First, I'd like to say this isn't a general question on the Facebook php/javascript sdk. I've successfully added the "Facebook login button" to a few little test projects.

My question is, what is the best way to show the user is wanting to log in with Facebook. Just because someone is logged in to Facebook when the visit my site, doesn't necessarily mean they want to login to my site with Facebook.

I know that after authorizing the user with a FB app, it redirects with a variety of $_GET variables, but if my user is returning to my site, and has already authorized my app, how can I create a "Facebook Login" button that basically 'says' If user clicks this button, pull Facebook user_profile, and use their info for login, else require Facebook login as normal.

I know I could create a button, forward to a page, set a session var, and redirect to the main page, but I'd like to create this effect without noticeable redirections; no redirections if possible.

Answer 1

I think you want to use FB.getLoginStatus. You'll asynchronously get a response telling you the auth state, and you can manually go from there (show their info, log them in, redirect if you want, etc).

From the SDK reference (https://developers.facebook.com/docs/reference/javascript/FB.getLoginStatus/):

FB.getLoginStatus(function(response) {
  if (response.status === 'connected') {
    // the user is logged in and has authenticated your
    // app, and response.authResponse supplies
    // the user's ID, a valid access token, a signed
    // request, and the time the access token 
    // and signed request each expire
    var uid = response.authResponse.userID;
    var accessToken = response.authResponse.accessToken;
  } else if (response.status === 'not_authorized') {
    // the user is logged in to Facebook, 
    // but has not authenticated your app
  } else {
    // the user isn't logged in to Facebook.
  }
 });