In the discretion of the authority, any issue of such revenue bonds may be secured by a trust indenture by and between the authority and a corporate trustee, which may be any trust company or bank having the powers of a trust company within or outside of the state. Such trust indenture may pledge or assign revenues and earnings to be received. Either the resolution providing for the issuance of revenue bonds or the trust indenture may contain such provisions for protecting and enforcing the rights and remedies of the bondholders as may be reasonable and proper and not in violation of law, including covenants setting forth the duties of the authority in relation to the acquisition of property, the construction of the project, the maintenance, operation, repair, and insurance of the project, and the custody, safeguarding, and application of all moneys; may also provide that any project shall be constructed and paid for under the supervision and approval of consulting engineers or architects employed or designated by the authority and satisfactory to the original purchasers of the bonds issued therefor; may also require that the security given by contractors and by any depositary of the proceeds of the bonds or revenues or other moneys be satisfactory to the purchasers; and may also contain provisions concerning the conditions, if any, upon which additional revenue bonds may be issued. It shall be lawful for any bank or trust company incorporated under the laws of this state to act as such depositary and to furnish such indemnifying bonds or pledge such securities as may be required by the authority. The indenture may set forth the rights and remedies of the bondholders and of the trustee and may restrict the individual right of action of bondholders as is customary in trust indentures securing bonds and debentures of corporations. In addition to the foregoing, the trust indenture may contain such other provisions as the authority may deem reasonable and proper for the security of the bondholders. All expenses incurred in carrying out the trust indenture may be treated as a part of the cost of maintenance, operation, and repair of the project or projects affected by the indenture.