Facebook Connect PHP session variable won't set - php

Question

I am using the Facebook PHP API 4.0 and trying to get the session variable to be set, so I can use the user's Facebook data.
The app, and Facebook approval page have all worked as expected, but the $session variable remains to be unset no matter what I try. I have tried to find the solution from similar questions on Stack with no success. This is the code I am using:
session_start();
//start fb login stuff
require_once( $config['basedir'].'/Facebook/FacebookSession.php' );
require_once( $config['basedir'].'/Facebook/FacebookRedirectLoginHelper.php' );
require_once( $config['basedir'].'/Facebook/FacebookRequest.php' );
require_once( $config['basedir'].'/Facebook/FacebookResponse.php' );
require_once( $config['basedir'].'/Facebook/FacebookSDKException.php' );
require_once( $config['basedir'].'/Facebook/FacebookRequestException.php' );
require_once( $config['basedir'].'/Facebook/FacebookAuthorizationException.php' );
require_once( $config['basedir'].'/Facebook/GraphObject.php' );
use Facebook\FacebookSession;
use Facebook\FacebookRedirectLoginHelper;
use Facebook\FacebookRequest;
use Facebook\FacebookResponse;
use Facebook\FacebookSDKException;
use Facebook\FacebookRequestException;
use Facebook\FacebookAuthorizationException;
use Facebook\GraphObject;
// init app with app id (APPID) and secret (SECRET)
FacebookSession::setDefaultApplication($fb_app, $fb_secret);
$helper = new FacebookRedirectLoginHelper( $config['baseurl'] );
try {
$session = $helper->getSessionFromRedirect();
} catch(FacebookRequestException $ex) {
// When Facebook returns an error
echo $ex;
} catch(\Exception $ex) {
// When validation fails or other local issues
echo $ex;
}
if ($session) {
echo 'Session var is finally being seen';
}
//end Facebook login stuff

Answer 1

The $session remains unset because you aren't logging the user in. You should modify the last part of the code to something like:
if ( isset( $session ) ) {
echo 'Session var is finally being seen';
} else {
// show login url
echo 'Login';
}
If the $session is not set, your code will ask the user to login. After they login, the $helper->getSessionFromRedirect(); part of your code should execute and set $session. See my tutorial on how to tackle this.
Edit:
If you are logging the user in from a different page, you need to make sure that $helper = new FacebookRedirectLoginHelper( '{your-url}' ); is the same on both pages. If they differ, then you will get a exception from the API related to redirect_uri mismatch.