Question

Users have been able to log into my website using their Facebook account, but then it suddenly stopped working properly.

I use the following standard Facebook JavaScript SDK code:

window.fbAsyncInit = function() {
  FB.init({
    appId      : '<MY_APP_ID>',
    status     : true, // check login status immediately
    cookie     : true, // enable cookies to allow the server to access the session
    xfbml      : false // because I don't use XFBML
  });
  FB.login(function(response) {
    // code that deals with `response`, whether null or not
  });
}

But if I cleared the browser cache, and triggered this code (after the Facebook library had loaded), the following would happen:

1. Facebook’s login dialog would pop up.
2. After entering credentials of a user that has access to this Facebook app, a dialog would ask whether I want to register a new login location.
3. Regardless of the action taken in the previous step, the dialog box displays the following error message:

An error may have occurred as part of the login process. You can close this window and try returning to the application, though it may ask you to log in again. This is probably due to a bug in the application.

FB.login’s response contains an error message. Inspecting the browser’s state, I can see that login information is stored within a Facebook cookie. Triggering the above code again, without clearing the cache, now succeeds.

Why doesn’t it work the first time around?

Answer 1

Due to Facebook’s OAuth 2.0 and HTTPS Migration, not using OAuth 2.0 after October 1, 2011 within JavaScript SDK will not work (properly).

To make the above example work, make sure that:

• your FB.init call sets oauth to true (see example usage):
• in the code that deals with the response:
  • you are reading the authResponse (not session) field of the FB.login’s response;
  • you are calling FB.getAuthResponse (not FB.getSession), and reading signedRequest from its response.