code: public final Long getExpiresInSeconds() {
      lock.lock();
      try {
        if (expirationTimeMilliseconds == null) {
          return null;
        }
        return (expirationTimeMilliseconds - clock.currentTimeMillis()) / 1000;
      } finally {
        lock.unlock();
      }
    }
docs: Returns the remaining lifetime in seconds of the access token (for example 3600 for an hour
  from now, or -3600 if expired an hour ago) or {@code null} if unknown.