Middleware and Filters

Middleware and Filters in CodeIgniter (CodeIgniter 4)

In CodeIgniter 4, Filters act like middleware. They allow you to run code before or after a request, commonly used for authentication, authorization, CSRF protection, and request modification.

1. What Are Filters?

• Code executed before or after a controller runs

• Used to protect routes

• Similar to middleware in Laravel

2. Filter Location

app/Filters/

3. Creating a Filter

Use Spark CLI:

php spark make:filter Auth

This creates:

app/Filters/Auth.php

4. Filter Example (Authentication)

namespace App\Filters;

use CodeIgniter\HTTP\RequestInterface;
use CodeIgniter\HTTP\ResponseInterface;
use CodeIgniter\Filters\FilterInterface;

class Auth implements FilterInterface
{
    public function before(RequestInterface $request, $arguments = null)
    {
        if (! session()->get('logged_in')) {
            return redirect()->to('/login');
        }
    }

    public function after(RequestInterface $request, ResponseInterface $response, $arguments = null)
    {
        // Optional post-processing
    }
}

5. Registering Filters

File:

app/Config/Filters.php

public $aliases = [
    'auth' => \App\Filters\Auth::class,
];

6. Applying Filters to Routes

Single Route

$routes->get('dashboard', 'Dashboard::index', ['filter' => 'auth']);

Route Group

$routes->group('admin', ['filter' => 'auth'], function($routes) {
    $routes->get('dashboard', 'Admin::dashboard');
});

7. Global Filters

Apply to all requests.

public $globals = [
    'before' => [
        'csrf',
    ],
    'after' => [
        'toolbar',
    ],
];

8. Filter Arguments

$routes->get('admin', 'Admin::index', ['filter' => 'role:admin']);

Filter:

public function before(RequestInterface $request, $arguments = null)
{
    if ($arguments[0] !== session()->get('role')) {
        return redirect()->back();
    }
}

9. Built-in Filters

10. API Authentication Filter Example

public function before(RequestInterface $request, $args = null)
{
    $token = $request->getHeaderLine('Authorization');

    if (! $token) {
        return service('response')
            ->setJSON(['error' => 'Unauthorized'])
            ->setStatusCode(401);
    }
}

11. Best Practices

✅ Use filters for authentication & authorization
✅ Keep filters lightweight
✅ Apply filters at route-level
❌ Avoid heavy logic in filters

Summary

• Filters = Middleware in CI4

• Used before/after requests

• Protect routes & APIs

• Centralized request control