All bonds issued by an authority may be executed by such officers of the authority and in such manner as shall be provided in the proceedings of the board whereunder the bonds shall be authorized to be issued. Any such bonds may be executed and delivered by an authority at any time and from time to time, shall be in such form and denominations and of such tenor and maturities, shall contain such provisions not inconsistent with the provisions of this article and shall bear such rate or rates of interest, payable and evidenced in such manner as may be provided by resolution of its board. Bonds of an authority may be sold at either public or private sale in such manner and at such price or prices and at such time or times as may be determined by the board to be most advantageous. The principal of or interest on any bonds issued or obligations assumed by an authority may thereafter at any time (whether before, at or after maturity of any such principal and whether at, after or not exceeding six months prior to the maturity of any such interest) and from time to time be refunded by the issuance of refunding bonds of the authority, which may be sold by the authority at public or private sale at such price or prices as may be determined by its board to be most advantageous or which may be exchanged for the bonds or other obligations to be refunded. An authority may pay all expenses, premiums and commissions which its board may deem necessary and advantageous in connection with any financing done by it. All bonds issued by an authority, unless registered as to principal, shall be construed to be negotiable instruments though payable from a specified source. All obligations created or assumed by an authority shall be solely and exclusively an obligation of the authority and shall not create an obligation or debt of any county or municipality or of the state; provided, that this sentence shall not be construed to release the original obligor from liability on any bond or other obligation assumed by an authority. Any bonds issued by an authority shall be limited or special obligations of the authority payable solely out of the revenues of the authority specified in the proceedings authorizing those bonds. Any such proceedings may provide that the bonds therein authorized shall be payable solely out of the revenues derived from the operation or leasing or sale of all property and facilities owned or operated by the authority or solely out of the revenues from the operation or leasing or sale of any one or more of such property and facilities, or parts thereof, regardless of the fact that those bonds may have been issued with respect to or for the benefit of only certain property and facilities of the authority. An authority may pledge for the payment of any of its bonds issued or obligations assumed the revenues from which such bonds or obligations are payable and may execute and deliver a trust indenture evidencing any such pledge or a mortgage and deed of trust conveying as security for such bonds or obligations the property and facilities, or any part of any thereof, the revenues or any part of the revenues from which are so pledged. Any mortgage and deed of trust or trust indenture made by an authority may contain such agreements as the board may deem advisable respecting the operation, leasing and maintenance of the property and the use of the revenues subject to such mortgage and deed of trust or affected by such trust indenture and respecting the rights, duties and remedies of the parties to any such instrument and the parties for the benefit of whom such instrument is made; provided, that no such instrument shall be subject to foreclosure unless the person to whom the property or facilities are leased by the authority operates for profit, in which event any such mortgage may be subject to foreclosure.