code: private void startAuthFlow(
        HttpServletResponse resp, PersistenceManager pm, ThreeLeggedFlow oauthFlow)
        throws IOException {
      pm.makePersistent(oauthFlow);
      String authorizationUrl = oauthFlow.getAuthorizationUrl();
      resp.sendRedirect(authorizationUrl);
    }
docs: Start the auth flow. Don't run any code after this method that will change the response object.