微信获取access_token和curl

public function get_wx_access_token()
    {
        //将access_token存在session/cookie中
        //如果access_token在session中并没有过期
        if (isset($_SESSION['access_token']) && $_SESSION['expire_time'] > time()) {
            return $_SESSION['access_token'];
        }
        //如果access_token不存在或者已经过期，重新获取access_token
        else {
            //$appid     = 'wx5486430ceb12f84a';
            // $appsecret = 'f52859525c6b799636d78bb49af14513';
            $url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=" . $this->appid . "&secret=" . $this->appsecret;
            $arr = $this->http_curl($url);
            //存到session中
            $access_token             = $arr['access_token'];
            $_SESSION['access_token'] = $arr['access_token'];
            $_SESSION['expire_time']  = time() + 7200;
            return $access_token;
        }
    }
protected function http_curl($url, $arr = '', $type = 'get', $res = 'json')
    {
        $ch = curl_init();
        //设置curl的参数
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        if ($type == 'post') {
            curl_setopt($ch, CURLOPT_POST, 1);
            curl_setopt($ch, CURLOPT_POSTFIELDS, $arr);
        }
        //采集
        $output = curl_exec($ch);
        if ($res == 'json') {
            if ($err = curl_errno($ch)) {
                //要在关闭之前获得curl_errno
                curl_close($ch);
                //请求失败，返回错误信息
                return $err;
            } else {
                //请求成功
                return json_decode($output, true);
            }
        }
    }