Really simple codeigniter access control

Question

I'm using the fresh new Codeigniter 3 framework but it seems that it lacks any Role Based Access Control List feature. I know that there are some libraries for that purpose but they seem overkill for my needs.

I use CAS for authorization so we can take this out of the equation. It seems to me that there are basically 3 approaches to this:

1. Using Sessions

2. Using Hooks

3. Using a Access Control List (ACL) library

The simpler, super basic approch that I have now is using Sessions like this in my Main controller:

(...)
public function index()
    {

        //Loading the CAS authentication library:
        $this->load->library('cas');
        $this->cas->force_auth();
        $user = $this->cas->user();

        //Seek for the user role in a database table
         $this->load->model("get_db");
         $role = $this->get_db->getPermissions($user->userlogin);

        //We save user information in the session
        $newData = array(
            'username' => $user->userlogin,
            'rol' => $role[0]->rol,
            'isLoggedIn' => TRUE
        );
        $this->session->set_userdata($newData);
(...)

And then I have a function that checks whether a user is logged in or not:

public function is_loggedIn(){
        $check_login = $this->session->userdata('isLoggedIn');

        if($check_login === FALSE)
        {
        //redirect('user');
        }
    }

And I call that function in every method in every controller. This is kinda unefficient. What would be a better approach to it? Bear in mind that my roles are a few ones and very basic so that a complex library would be overkill.

Thanks.