callmez\wechat\sdk\Wechat::refreshOauth2AccessToken PHP Method

    public function refreshOauth2AccessToken($refreshToken, $grantType = 'refresh_token')
    {
        $result = $this->httpGet(self::WECHAT_OAUTH2_ACCESS_TOKEN_REFRESH_URL . http_build_query(['appid' => $this->appId, 'grant_type' => $grantType, 'refresh_token' => $refreshToken]));
        return isset($result['errmsg']) ? false : $result;
    }