All real property of an authority shall be exempt from levy and sale by virtue of an execution; and no execution or other judicial process shall issue against the same nor shall any judgment against an authority be a charge or lien upon its real property, provided that this Code section shall not apply to or limit the right of obligees to foreclose or otherwise enforce any mortgage of an authority or the right of obligees to pursue any remedies for the enforcement of any pledge or lien given by an authority on its rents, fees, or revenues.