Create read only user once PostgresSQL procedure

create_temp_user.sql

CREATE OR REPLACE PROCEDURE create_temp_user(user_id VARCHAR)
    LANGUAGE plpgsql
    AS $$
    BEGIN
        IF NOT EXISTS (SELECT 1 FROM pg_user WHERE usename = user_id) THEN
            EXECUTE 'CREATE USER ' || user_id || ' WITH PASSWORD DISABLE';
            EXECUTE 'GRANT SELECT ON ALL TABLES IN SCHEMA public TO ' || user_id;
            EXECUTE 'GRANT USAGE ON SCHEMA public TO ' || user_id;
            EXECUTE 'ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO ' || user_id;
        END IF;
    END;
    $$;