Facebook PHP SDK 4.0.8

<?php

// require the Composer autoload
require 'vendor/autoload.php';

// start session
session_start();

// init app with app id and secret
Facebook\FacebookSession::setDefaultApplication('APP_ID', 'APP_SECRET');

// create new redirect login helper
// use destination URL to redirect to after login
$helper = new Facebook\FacebookRedirectLoginHelper('http://example.com/');

// see if a existing session exists
if (isset($_SESSION) && isset($_SESSION['fb_token']))
{
  // create new session from saved access_token
  $session = new Facebook\FacebookSession($_SESSION['fb_token']);
  
  // validate the access_token to make sure it's still valid
  try
  {
    if(!$session->validate())
    {
      $session = null;
    }
  } catch (Exception $e) {
    // catch any exceptions
    $session = null;
  }
  
} else {
  // no session exists
  
  try {
    $session = $helper->getSessionFromRedirect();
  } catch(Facebook\FacebookRequestException $e) {
    // When Facebook returns an error
    // handle this better in production code
    print_r($e);
  } catch(Exception $e) {
    // When validation fails or other local issues
    // handle this better in production code
    print_r($e);
  }
  
}

// see if we have a session
if (isset($session))
{
  // save the session
  $_SESSION['fb_token'] = $session->getToken();
  // create a session using saved token or the new one we generated at login
  $session = new Facebook\FacebookSession($session->getToken());
  
  // graph api request for user data
  $request = new Facebook\FacebookRequest($session, 'GET', '/me');
  $response = $request->execute();
  // get response
  $graphObject = $response->getGraphObject(Facebook\GraphUser::className());
  
  // print profile data
  echo '<pre>' . print_r($graphObject, 1) . '</pre>';
  
  // print logout url using session and redirect_uri (logout.php page should destroy the session)
  echo '<a href="' . $helper->getLogoutUrl($session, 'http://example.com/logout.php') . '">Logout</a>';
  
} else {
  // show login url
  // pass required scope here
  echo '<a href="' . $helper->getLoginUrl(array('email', 'user_friends')) . '">Login</a>';
}