def to_header(self):
        """Convert the stored values into a WWW-Authenticate header."""
        d = dict(self)
        auth_type = d.pop("__auth_type__", None) or "basic"
        return "%s %s" % (
            auth_type.title(),
            ", ".join(
                [
                    "%s=%s"
                    % (
                        key,
                        quote_header_value(
                            value, allow_token=key not in self._require_quoting
                        ),
                    )
                    for key, value in iteritems(d)
                ]
            ),
        )