The city attorney of a city of the metropolitan class shall have the power to: (1) Intervene in any suit or proceeding when the rights of the city are involved or where the city is a proper party; (2) Waive the issuance and service of summons and may enter a voluntary appearance when in the city attorney's opinion the interests of the city may require it; and (3) Confess judgment, but only when authorized by the city council.