Immigration Advisory Program Authorization Act of 2018 or the IAP Authorization Act of 2018 (Sec. 2) This bill amends the Homeland Security Act of 2002 to authorize within U.S. Customs and Border Protection (CBP) an immigration advisory program for CBP officers, pursuant to an agreement with a host country, to assist air carriers and security employees at foreign airports review traveler information during the processing of U.S.-bound flights. CBP shall provide Congress with: a copy of any host country agreement within 60 days of such agreement entering into force which shall include information on anticipated homeland security benefits, costs, CBP personnel needs, and possible terrorist and criminal travel; and a copy of, and a justification for, any substantially amended agreement within 30 days of such agreement entering into force.