Passing custom-header arguments to Knp SnappyBundle

I'm using Knp SnappyBundle in Symfony 4.

I'm having trouble passing the custom-header argument (--custom-header <name> <value>) to wkhtmltopdf through yaml or as option in request.

Here is what I'm trying, which seems to fail:

knp_snappy:
  temporary_folder: "%kernel.cache_dir%/snappy"
  pdf:
    enabled: true
    binary: xvfb-run wkhtmltopdf
    options:
      - { name: 'custom-header', value: '%app_auth_header_name%' '%app_auth_header_token%'  }

I've also tried passing the values as an array, but that also fails.

I have solved it partially, unfortunately not by yaml, but direcly in code example:

   public function getPdfBinary($url, Pdf $pdfService): PdfResponse
    {
        $url = urldecode($url);
        $res = new PdfResponse($pdfService->getOutput($url, ['custom-header' =>
            [ 'X-Authorization' => 'mytoken' ] ]),'output.pdf');
        return $res;

yaml expect scalar value of custom-header...