Read only creation of a user for RDS postgres cluster

readonly_postgres.sql

DROP ROLE IF EXISTS readaccess;
CREATE ROLE readaccess;

GRANT USAGE ON SCHEMA public TO readaccess;

ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO readaccess;

GRANT SELECT ON ALL TABLES IN SCHEMA public TO readaccess;

DROP USER IF EXISTS readonly;
CREATE USER readonly WITH PASSWORD 'secret';
GRANT readaccess TO readonly;