The bonds of the authority shall be signed by its president and attested by its secretary and the seal of the authority shall be affixed thereto or a facsimile of such seal shall be printed or otherwise reproduced thereon; provided, that a facsimile of the signature of one, but not both, of said officers may be printed or otherwise reproduced on any such bonds in lieu of being manually subscribed thereon and a facsimile of the signatures of both of the officers may be printed or otherwise reproduced on such bonds in lieu of being manually affixed thereof if the authority, in its proceedings with respect to issuance of the bonds, provides for manual authentication of such bonds. The State Treasurer shall be registrar, transfer agent, and paying agent for the bonds. The State Treasurer may designate named individuals who are employees of the state and who are assigned to the Finance Department or the State Treasurer's office to authenticate the bonds. Any bonds of the authority may be executed and delivered by it at any time and from time to time and shall be in such form or forms and such denomination or denominations and of such tenor and maturity or maturities, shall bear such rate or rates of interest, which may be variable rates, shall be payable at such times and evidenced in such manner, and may contain such other provisions not inconsistent herewith, all as may be provided by the resolution of the board of directors of the authority under which such bonds are authorized to be issued; provided, that no bond of the authority shall have a specified maturity date later than twenty years after its date. Any bond of the authority may be made subject to redemption at the option of the authority at such times and after such notice and on such conditions and at such redemption price or prices as may be provided in the resolution under which it is authorized to be issued; provided, that those bonds of the authority having specified maturity dates more than 10 years after their date shall be made subject to redemption at the option of the authority not later than the end of the tenth year after their date, and on any interest payment date thereafter, under such terms and conditions and at such redemption price or prices as may be provided in the resolution under which such bonds are authorized to be issued. Bonds of the authority may be sold at such price or prices and at such time or times as the board of directors of the authority may consider advantageous, either at public or private sale and by negotiation or by competitive bid. Bonds of the authority sold by competitive bid must be sold, whether on sealed bids or at public auction, to the bidder whose bid reflects the lowest true interest cost to the authority for the bonds being sold, computed from their date to their respective maturities; provided, that if no bid acceptable to the authority is received, it may reject all bids. The authority may fix the terms and conditions under which each sale of bonds may be held; provided, that such terms and conditions shall not conflict with any of the requirements of this article. Subject to the provisions and limitations contained in this article, the authority may from time to time sell and issue refunding bonds for the purpose of refunding any matured or unmatured bonds of the authority then outstanding. Such refunding bonds shall be subrogated and entitled to all priorities, rights and pledges to which the bonds refunded thereby were entitled. Provided, however, that no refunding bonds shall be issued unless the present value of all debt service on the refunding bonds, computed with a discount rate equal to the true interest rate of the refunding bonds and taking into account all underwriting discount and other issuance expenses, shall not be greater than 95% of the present value of all debt service on the bonds to be refunded, computed using the same discount rate and taking into account the underwriting discount and other issuance expenses originally applicable to such bonds, determined as if such bonds to be refunded were paid and retired in accordance with the schedule of maturities, considering mandatory redemption as a scheduled maturity, provided at the time of their issuance. Provided further, that the average maturity of the refunding bonds, as measured from the date of issuance of such refunding bonds, shall not exceed by more than three years the average maturity of the bonds to be refunded, as also measured from such date of issuance, with the average maturity of any principal amount of bonds to be determined by multiplying the principal of each maturity by the number of years, including any fractional part of a year, intervening between such date of issuance and each such maturity, taking the sum of all such products, and then dividing such sum by the aggregate principal amount of bonds for which the average maturity is to be determined. The authority may pay out of the proceeds of the sale of its bonds attorneys' fees and the expenses of issuance which the board of directors may deem necessary and advantageous in connection with the issuance of such bonds. Bonds issued by the authority shall not be general obligations of the authority but shall be payable solely out of the funds appropriated and pledged thereof in Section 11-85-108. As security for the payment of the principal of and interest on the bonds issued by it, the authority is hereby authorized and empowered to pledge for payment of such principal and interest the funds that are appropriated and pledged in Section 11-85-108 for payment of such principal and interest. All such pledges made by the authority shall take precedence in the order of the adoption of the resolutions containing such pledges; provided, that each pledge for the benefit of refunding bonds shall have the same priority as the pledge for the benefit of the bonds refunded thereby. All contracts made and all bonds issued by the authority pursuant to this article shall be solely and exclusively obligations of the authority and shall not constitute or create an obligation or debt of the State of Alabama. All bonds issued by the authority and the income therefrom shall be exempt from all taxation in the state. Any bonds issued by the authority may be used by the holder thereof as security for any funds belonging to the state, or to any political subdivision, instrumentality, or agency of the state, in any instance where security for such deposits may be required by law. Unless otherwise directed by the court having jurisdiction thereof, or the document that is the source of authority, a trustee, executor, administrator, guardian, or one acting in any other fiduciary capacity may, in addition to any other investment powers conferred by law and with the exercise of reasonable business prudence, invest trust funds in bonds of the authority. Neither a public hearing nor consent of the Department of Finance of the state or any other department or agency shall be a prerequisite to the issuance of the bonds by the authority. The bonds issued under this article shall be legal investments for funds of the Teachers' Retirement System of Alabama, the Employees' Retirement System of Alabama, and the State Insurance Fund.