Convert the stored values into a WWW-Authenticate header.

def _auth_header(self, type, **options):
        """Convert the stored values into a WWW-Authenticate header."""
        return '%s %s' % (type.title(), ', '.join((
            '%s=%s' % (key, quote_header_value(
                value, allow_token=key not in _require_quoting))
            for key, value in options.items()
        )))