Login with Facebook using PHP [Step by Step]

<?php

   session_start();

   // added in v4.0.0
   require_once 'autoload.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;
   use Facebook\Entities\AccessToken;
   use Facebook\HttpClients\FacebookCurlHttpClient;
   use Facebook\HttpClients\FacebookHttpable;

   // init app with app id and secret
   FacebookSession::setDefaultApplication( 'your app ID','App Secrete ' );

   // login helper with redirect_uri
   $helper = new FacebookRedirectLoginHelper('http://www.phpcodingstuff.com/' );

   try {
      $session = $helper->getSessionFromRedirect();
   }catch( FacebookRequestException $ex ) {
      // When Facebook returns an error
   }catch( Exception $ex ) {
      // When validation fails or other local issues
   }

   // see if we have a session
   if ( isset( $session ) ) {
      // graph api request for user data
      $request = new FacebookRequest( $session, 'GET', '/me' );
      $response = $request->execute();

      // get response
      $graphObject = $response->getGraphObject();
      $fbid = $graphObject->getProperty('id');           // To Get Facebook ID
      $fbfullname = $graphObject->getProperty('name');   // To Get Facebook full name
      $femail = $graphObject->getProperty('email');      // To Get Facebook email ID

      /* ---- Session Variables -----*/
      $_SESSION['FBID'] = $fbid;
      $_SESSION['FULLNAME'] = $fbfullname;
      $_SESSION['EMAIL'] =  $femail;

      /* ---- header location after session ----*/
      header("Location: index.php");
   }else {
      $loginUrl = $helper->getLoginUrl();
      header("Location: ".$loginUrl);
   }
?>