code: protected String createRememberMeKey(USER_ENTITY userEntity, USER_BEAN userBean) {
          return String.valueOf(userBean.getUserId()); // as default (override if it needs)
      }
docs: Create remember-me key for the user. <br>
  You can change user key's structure by override. #change_user_key
  @param userEntity The selected entity of login user. (NotNull)
  @param userBean The user bean saved in session. (NotNull)
  @return The string expression for remember-me key. (NotNull)