code: public function isRequestValid ($id, $secret)
  	{
  		$data = array
  		(
  			'id' => $id,
  			'secret' => $secret
  		);
  
  		$url = $this->getSignedURL (self::PAYMENT_GATEWAY_URL.'check/', $data);
  
  		$data = $this->file_get_contents ($url);
  		if ($data)
  		{
  			if ($data == '1')
  			{
  				return true;
  			}
  		}
  
  		return false;
  	}
docs: /*
  Use this method to check if a callback is valid