Okla. Stat. tit. 21, § 577

Whenever an action or proceeding is authorized by law to be prosecuted or defended in the name of the people, or of any public officer, board of officers or municipal corporation, on behalf of another party, the Attorney-General or district attorney, or attorney of such public officer or board or corporation may permit any proceeding therein to be taken in his name by an attorney to be chosen by the party in interest.