/**
  * 根据 AuthorizationCode 获取 AccessToken
  *
  * @param code AuthorizationCode
  */
 public Observable<LoginData> getToken(String code) {
   return mAccountApi
       .getToken(
           Constants.APP_KEY,
           Constants.APP_SECRET,
           REQUEST_REDIRECT_URI_MINE,
           REQUEST_GRANT_TYPE_GET,
           code)
       .compose(flatResult());
 }