CI4 Filter before method throw for page unauthorized

I'm able to filter request to my rest api using ci4 filter.
But the problem is, I dont understand how to throw the error for showing page unauthorized like in http message.

PHP Code:

class Authorization implements FilterInterface {
  public function before(RequestInterface $request){
    $token = $request->getServer('HTTP_AUTHORIZATION')
    if($token == null){
      // How can I send the response that showing unauthorized 401?
      // 
    }
  }
}

This class is not extending resource controller so first you need to do that i did 

use CodeIgniter\HTTP\RequestInterface;
use CodeIgniter\HTTP\ResponseInterface;
use CodeIgniter\Filters\FilterInterface;
use CodeIgniter\RESTful\ResourceController;
use CodeIgniter\API\ResponseTrait;

class AuthFilter extends ResourceController implements FilterInterface{
public $response;

use ResponseTrait;

public function before(RequestInterface $request, $arguments = null)

    {
         $this->response = \Config\Services::response(); // if you don't do this response will be undefined and error will be thrown
         if something not authorised

         $description = lang('Validation.token_invalid');

         return $this->failUnauthorized($description);

    }

}