code: public OauthGetTokenResponse getToken(String code) {
          BeanUtil.requireNonNull(code, "code is null");
          OauthGetTokenResponse response = null;
          String url = BASE_API_URL + "sns/oauth2/access_token?appid=" + this.config.getAppid() + "&secret=" + this.config.getSecret() + "&code=" + code + "&grant_type=authorization_code";
          BaseResponse r = executeGet(url);
          String resultJson = isSuccess(r.getErrcode()) ? r.getErrmsg() : r.toJsonString();
          response = JSONUtil.toBean(resultJson, OauthGetTokenResponse.class);
          return response;
      }
docs: 用户同意授权后在回调url中会得到code，调用此方法用code换token以及openid，所以如果仅仅是授权openid，到这步就结束了
  
  @param code 授权后得到的code
  @return token对象