Section 23. The department of the state auditor shall biennially make an audit of the accounts of the authority and make a report thereon to the directors, the governor and the general court. In making said audits, said department of the state auditor may call upon any of the departments, commissions, officers and agencies of the commonwealth for such information as may be needed in the course of making such audits. The state auditor may employ such auditors, accountants and other assistants as he deems necessary for carrying out said duties, and chapter 31 and the rules made thereunder shall not apply to such employees. The commonwealth shall be reimbursed by the authority for the cost of the audit.