How to redirect from controller constructor?

I have these code in the files.

index.php

<?php
$App = new \Slim\App();
$App->get('/', '\Modules\Home\Controllers\IndexController:indexAction');
$App->get('/admin', '\Modules\Admin\Controllers\IndexController:indexAction');

Modules/Home/Controllers/IndexController.php

<?php


namespace Modules\Home\Controllers;

use \Psr\Http\Message\ServerRequestInterface;
use \Psr\Http\Message\ResponseInterface;

/**
 * Home main controller.
 *
 * @author Vee W.
 */
class IndexController extends \Modules\Core\Controllers\BaseController
{


    public function indexAction(ServerRequestInterface $request, ResponseInterface $response)
    {
        // this is home page. just send user to /admin page.
        return $response->withStatus(301)->withHeader('Location', 'admin');
    }// indexAction


}

Modules/Admin/Controllers/IndexController.php

<?php


namespace Modules\Admin\Controllers;

use \Psr\Http\Message\ServerRequestInterface;
use \Psr\Http\Message\ResponseInterface;

/**
 * Admin home page or admin dashboard.
 *
 * @author Vee W.
 */
class IndexController extends \Modules\Core\Controllers\AdminController
{


    public function indexAction(ServerRequestInterface $request, ResponseInterface $response)
    {
        //echo 'admin page.';
        return $response;
    }// indexAction


}

Modules/Core/Controllers/AdminController.php

<?php


namespace Modules\Core\Controllers;

use \Psr\Http\Message\ServerRequestInterface;
use \Psr\Http\Message\ResponseInterface;
use \Interop\Container\ContainerInterface;

/**
 * The administrator base controller that all admin page should extends this.
 *
 * @author Vee W.
 */
abstract class AdminController extends \Modules\Core\Controllers\BaseController
{


    public function __construct(ContainerInterface $ci)
    {
        parent::__construct($ci);
        $this->ci = $ci;

        $UserDb = new \Modules\Admin\Models\UsersDb($this->Db);
        if (!$UserDb->isUserLoggedIn()) {
            header('Location: admin/login');
            http_response_code(302);
        }
    }// __construct


}

I want to redirect not logged in users from this base controller (Modules/Core/Controllers/AdminController.php) but I cannot redirect the user.
How to redirect from controller constructor?

Seems a bit weird to me to do so. But if you really want to you could indeed set the header. You just have to exit the code after doing so to stop the application from running anyway.