CREATE FUNCTION auth_user(text, text) RETURNS bool AS '
DECLARE
  salt text;
BEGIN
  SELECT INTO salt substring(passwd, 1, 2) FROM users WHERE usename = $1;
  IF NOT FOUND THEN
    RETURN false;
  END IF;

  PERFORM * FROM users WHERE usename = $1 AND passwd = crypt($2, salt);
  IF NOT FOUND THEN
    RETURN false;
  END IF;

  RETURN true;
END;
' LANGUAGE PLPGSQL;