Bonds and securities of all kinds heretofore or hereafter authorized, issued by any issuing corporation or district (hereinafter called the "issuer" and as hereinafter specified), whether such bonds and securities be issued for such issuer itself or for any other taxing or assessment district within its limits, and whether payable in whole or in part out of and from general taxes or payable in whole or in part out of and from the earnings to be derived from any utility, system, construction, work, or works, belonging to or operated by any such issuer, or payable in whole or in part out of and from "local" or "benefit" assessments upon lands within any assessment district or assessment subdivision within any such issuer, may be sold to the United States government or to any department, corporation or agency thereof by private sale without giving any prior notice thereof by publication or otherwise and in such manner as the governing authority of such issuer may provide: PROVIDED, Only that bonds or other securities sold at private sale under the authority of this chapter shall bear interest at a rate or rates as authorized by the issuer and that all bonds and securities sold and issued under the authority of this chapter shall be sold, if now required by existing law, at not less than par and accrued interest.