Cannot access request headers in controller

Hello. I am just having a hard time working with request headers. I did a custom Controller which extends CodeIgniter\Controller. In the constructor (public function initController(\CodeIgniter\HTTP\RequestInterface $request,.....)  I try using the function $request->getHeader('any-header'); and they always return an empty object. Am I doing something wrong? Using the function $request->headers(); crashes because of error "Call to undefined method", even using $this->request->getHeader("any-header"); 
As a workaround I used php function getallheaders(). I'd like using the codeigniter functions. Any clue to fix this?