 fail_validate()离线验证结果错误

public function fail_validate($challenge, $validate, $seccode) {
    if(md5($challenge) == $validate){
        return 1;
    }else{
        return 0;
    }
}
此处验证错误 $seccode也没使用到，改成md5($this->private_key . 'geetest' . $challenge) == $validate才能正常验证