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?
      // 
    }
  }
}