The State of Nebraska does covenant and agree with the holders of bonds issued by an authority that the state will not limit or alter the rights hereby vested in an authority to acquire, maintain, construct, reconstruct, and operate projects, to establish and collect such rates, rentals, tolls, charges, license fees, and other fees as may be convenient or necessary to produce sufficient revenue to meet the expense of maintenance and operation of such projects and to fulfill the terms of any agreements made with holders of bonds of the authority. The state will also not in any way impair the rights and remedies of the bondholders until the bonds together with interest thereon and with interest on any unpaid installments of interest, and all costs and expenses in connection with any action or proceedings by or on behalf of the bondholders, are fully met and discharged. The provisions of section 3-239 and the Cities Airport Authorities Act and of the proceedings authorizing bonds thereby shall constitute a contract with the holders of the bonds.