Any district may submit to the attorney general any bonds issued under this article after all proceedings for their issuance have been taken. Upon submission the attorney general shall examine into and give an opinion upon the validity of the bonds and the regularity of all proceedings in connection therewith. If the proceedings conform to the provisions of this article, and the bonds when delivered and paid for will constitute binding and legal obligations of the district according to the terms thereof, the attorney general shall certify in substance upon the back of each of the bonds that it is issued in accordance with the constitution and laws of this state.