def _process_allow_headers(self, req, resp, requested_headers):
        """Adds the Access-Control-Allow-Headers header to the response,
        using the cors settings to determine which headers are allowed.

        Returns:
            True if all the headers the client requested are allowed.
            False if some or none of the headers the client requested are allowed.
        """
        if not requested_headers:
            return True
        elif self._cors_config['allow_all_headers']:
            self._set_allowed_headers(resp, requested_headers)
            return True

        approved_headers = []
        for header in requested_headers:
            if header.lower() in self._cors_config['allow_headers_list']:
                approved_headers.append(header)
            elif self._cors_config.get('allow_headers_regex'):
                if self._cors_config['allow_headers_regex'].match(header):
                    approved_headers.append(header)

        if len(approved_headers) == len(requested_headers):
            self._set_allowed_headers(resp, approved_headers)
            return True

        return False
Adds the Access-Control-Allow-Headers header to the response,
        using the cors settings to determine which headers are allowed.

        Returns:
            True if all the headers the client requested are allowed.
            False if some or none of the headers the client requested are allowed.