从iframe获取Codeigniter SESSION用户

I want get CI SESSION from my iframe app, in same domain my code like this on CI and session is running

public function ceklogin()
{
    if(isset($_POST['login'])){
        $user = $this->input->post('user',true);
        $pass = $this->input->post('pass',true);
        $cek = $this->web->proseslogin($user,$pass);
        $hasil = count($cek);           

        if ($hasil > 0){                
        $pelogin = $this->db->get_where('tb_user',array('username' => $user,'password' => $pass))->row();               
            $level = $pelogin->level;               
            $data= array ('level' => $level,
                                'logged_in'=> true,
                                'user_id'=>$pelogin->id,
                                'namanya'=>$pelogin->nama_lengkap,
                                'levelnya'=>$pelogin->level,
                                'kec_id_user'=>$pelogin->kec_id_user);

            $this->session->set_userdata($data);

        $this->input->set_cookie("idckec","kec_id_user"); //test set cookies
        $_SESSION['idkec'] = "kec_id_user"; //test set manual session


            if($pelogin->level == 'Admin'){                     
                redirect('index.php/dashboard');

            }elseif($pelogin->level == 'User'){

                redirect('index.php/dashboard?m='.$_SESSION[idkec]);

            }elseif($pelogin->level == 'Lain-lain'){

                redirect('lain-lain');
            }

            $this->session->set_flashdata('benar', 'login berhasil');
            //redirect('dashboard');
        }else{


            $this->session->set_flashdata('salah', 'Username dan Password tidak valid, coba ulangi!!!');
            redirect('index.php/admin','refresh');
        }

and in iframe i want to get CI Session

    session_start(); 
echo $_SESSION["idkec"]; //Notice: Undefined index: idkec in ...
echo $_COOKIE["idckec"]; //Notice: Undefined index: idckec in....

how can i get CI Session? thanks

really apreciated

Setting:

//$_SESSION['idkec'] = "kec_id_user"; //test set manual session
$this->session->set_userdata('idkec', 'something');

Getting:

//session_start(); // don't do this
echo $this->session->userdata('idkec');

More:

https://www.codeigniter.com/user_guide/libraries/sessions.html