Verify/validate User access for android app using facebook SDK at server side in PHP? -

i have android app. user can access app using facebook login. once user logged in, data/activity push web server using php. wanted validate user access app while accessing app. wanted check user app access status using access token when request comes php web server. main aim deny fake users request android web server security purpose. can me sort out problem . in advance..

<?php  try{     require_once(dirname(__file__) . '\facebook-php-sdk\src\facebook\facebook.php' ); } catch(exception $o){         print_r($o); } $config = array(     'appid' => '123456',     'secret' => '5ca2b11ea4c8sdsdsd',     'allowsignedrequest' => false // optional should set false non-canvas apps );  $facebook = new facebook($config); $user_id = $facebook->getuser(); $user_id = '123456';  if($user_id) {      // have user id, logged in user.     // if not, we'll exception, handle below.     try {         $ret_obj = $facebook->api('/'.$user_id.'/feed', 'post',             array(                 'link' => 'www.example.com',                 'message' => 'posting php sdk!'             ));          // $ret_obj = $facebook->api('/me/feed', 'post',         //     array(         //         'access_token' => $facebook->getaccesstoken(),         //         'link' => 'www.example.com',         //         'message' => 'posting php sdk!'         //     ));         echo '<pre>post id: ' . $ret_obj['id'] . '</pre>';          // give user logout link         echo '<br /><a href="' . $facebook->getlogouturl() . '">logout</a>';     } catch(facebookapiexception $e) {         // if user logged out, can have         // user id though access token invalid.         // in case, we'll exception, we'll         // ask user login again here.         echo "<pre>";var_dump($e);         $login_url = $facebook->getloginurl( array(             'scope' => 'publish_stream'         ));         echo 'please <a href="' . $login_url . '">login.</a>';         error_log($e->gettype());         error_log($e->getmessage());     } } else {      // no user, print link user login     // post user's wall, need publish_stream permission     // we'll use current url redirect_uri, don't     // need specify here.     $login_url = $facebook->getloginurl( array( 'scope' => 'publish_stream' ) );     echo 'please <a href="' . $login_url . '">login.</a>';  }?>