Creating a Facebook Page Tab App using the Facebook PHP SDK 4.0.x. This is a example how to create a likegate.

fb_tab_app_likegate_4.0.x.php

<?php
// include lines 1-65 from https://gist.github.com/niraj-shah/fcd17411def017e3aefc here

// see if the viewer has liked the page
if ( $pageHelper->isLiked() ) {

  // see if we have a session
  if ( isset( $session ) ) {
    
    // show logged-in user id
    echo 'User Id: ' . $pageHelper->getUserId();
    
    // graph api request for user data
    $request = new FacebookRequest( $session, 'GET', '/me' );
    $response = $request->execute();
    // get response
    $graphObject = $response->getGraphObject()->asArray();
    
    // print profile data
    echo '<pre>' . print_r( $graphObject, 1 ) . '</pre>';
    
    // print logout url, target = _top to break out of page frame
    echo '<a href="' . $helper->getLogoutUrl( $session, 'http://sites.local/php-sdk-4.0/redirect.php' ) . '" target="_top">Logout</a>';
    
  } else {
    // show login url, target = _top to break out of page frame
    echo '<a href="' . $helper->getLoginUrl( array( 'email', 'user_friends' ) ) . '" target="_top">Login</a>';
  }

} else {
  // show likegate
  echo '<h1>Please Like the page to continue</h1>';
}