code: public function getSelectedHeaderChecker(array $selected_header_checkers)
      {
          $result = [];
          foreach ($selected_header_checkers as $alias) {
              Assertion::keyExists($this->header_checkers, $alias, sprintf('The header checker alias "%s" is not supported.', $alias));
              $result[] = $this->header_checkers[$alias];
          }
  
          return $result;
      }
docs: @param string[] $selected_header_checkers
  
  @return \Jose\Checker\HeaderCheckerInterface[]