session_start();
require_once(ABSPATH . 'facebook-php-sdk-v4-4.0-dev/src/Facebook/FacebookSession.php');
require_once(ABSPATH . 'facebook-php-sdk-v4-4.0-dev/src/Facebook/FacebookRequest.php');
require_once(ABSPATH . 'facebook-php-sdk-v4-4.0-dev/src/Facebook/FacebookResponse.php');
require_once(ABSPATH . 'facebook-php-sdk-v4-4.0-dev/src/Facebook/FacebookSDKException.php');
require_once(ABSPATH . 'facebook-php-sdk-v4-4.0-dev/src/Facebook/FacebookRequestException.php');
require_once(ABSPATH . 'facebook-php-sdk-v4-4.0-dev/src/Facebook/GraphObject.php');
require_once(ABSPATH . 'facebook-php-sdk-v4-4.0-dev/src/Facebook/FacebookRedirectLoginHelper.php');
require_once(ABSPATH . 'facebook-php-sdk-v4-4.0-dev/src/Facebook/FacebookAuthorizationException.php');
require_once(ABSPATH . 'facebook-php-sdk-v4-4.0-dev/src/Facebook/FacebookJavaScriptLoginHelper.php');

use FacebookFacebookSession;
use FacebookFacebookJavaScriptLoginHelper;
use FacebookFacebookRedirectLoginHelper;
use FacebookFacebookRequest;
use FacebookFacebookResponse;
use FacebookFacebookSDKException;
use FacebookFacebookRequestException;
use FacebookFacebookAuthorizationException;
use FacebookGraphObject;

FacebookSession::setDefaultApplication('172357792955421', 'b0a5bc2aeb8b2a8712c0af6f01e45c1a');

$helper = new FacebookJavaScriptLoginHelper();
try {
  $session = $helper->getSession();
} catch(FacebookRequestException $ex) {
  echo 'Facebook returns an error';
} catch(Exception $ex) {
  echo 'When validation fails or other local issues';
}
if ($session)
  echo 'logged in';
else
  echo 'not logged in';

require_once( ABSPATH . 'facebook-php-sdk-v4-4.0-dev/autoload.php' );