Facebook - How to get user id in profile tab ?

Facebook documentation is soo bad :(
After a while searching I found this:

You must have turned on all items in migration in app settings ! (sep. 2010)

    public function parse_signed_request($signed_request, $secret) {
      list($encoded_sig, $payload) = explode('.', $signed_request, 2);
   
      // decode the data
      $sig = $this->base64_url_decode($encoded_sig);
      $data = json_decode($this->base64_url_decode($payload), true);
   
      if (strtoupper($data['algorithm']) !== 'HMAC-SHA256') {
        error_log('Unknown algorithm. Expected HMAC-SHA256');
        return null;
      }
   
      // check sig
      $expected_sig = hash_hmac('sha256', $payload, $secret, $raw = true);
      if ($sig !== $expected_sig) {
        error_log('Bad Signed JSON signature!');
        return null;
      }
   
      return $data;
    }
   
    public function base64_url_decode($input) {
      return base64_decode(strtr($input, '-_', '+/'));
    }

$aData = parse_signed_request($_REQUEST['signed_request'],APP_SECRET);
$iUserId = $aData['user_id'];