The President is authorized (subject to the succeeding provisions of this section) to enter into agreements establishing totalization arrangements between the social security system established by this subchapter and the social security system of any foreign country, for the purposes of establishing entitlement to and the amount of old-age, survivors, disability, or derivative benefits based on a combination of an individual’s periods of coverage under the social security system established by this subchapter and the social security system of such foreign country.