code: protected String setOauth2LoginState(HttpServletRequest req, HttpServletResponse resp, String authzEndpoint){
          String state = UUID.randomUUID().toString().replace("-","");
          req.getSession().setAttribute("oauth2_login_state", state);
          authzEndpoint = Urls.appendQueryString(authzEndpoint,"state",state);
          return authzEndpoint;
      }
docs: 设置跳转到登录页面时的<code>state</code>参数。
  
  默认生成一串随机{@link UUID},并去掉'-'符号作为<code>state</code>。
  
  @see #checkOauth2LoginState(HttpServletRequest, HttpServletResponse)