All claims presented against the city by persons furnishing materials, rendering services or performing labor, or for any other contractual purpose, shall be audited, before payment, by the finance department, which is designated as auditing officer. Such claims shall be prepared for audit and payment on a form and in the manner prescribed by the division of municipal corporations in the State Auditor’s Office. The form shall provide for the authentication and certification by such auditing officer that the materials have been furnished, the services rendered or the labor performed as described, and that the claim is a just, due and unpaid obligation against the city, and no claim shall be paid without such authentication and certification; provided, that the certificates as to claims of officers and employees of the city, for services rendered, shall be made by the person charged with the duty of preparing and submitting vouchers for the payment of services, and they shall certify that the claim is just, true and unpaid, which certificate shall be part of the voucher. (1957 code § 1.39.010.)