Codeigniter 4 form validation example, please.

Hello.
I'm loosing my head now with something I cannot achieve.

Imagine a view with a simple form.
A controller with 2 methods: one to echo the view. The other to process the form after submission.

Controller (home):

PHP Code:

public function index(){        
    return view('form');
}

public function submission(){
    $result = $this->validate([
        'username' => 'required',
        'password' => 'required'
    ]);

    if(!$result){
        return redirect()->back()->withInput();
    } else {
        echo 'Submission OK!';
    }
} 


View (form)

PHP Code:

<?= $this->validator->listErrors() ?>


    <?= form_open('home/submission')?>

    <div>        
        <input type="text" name="username" value="<?= old('username') ?>">
    </div>
    <div>        
        <input type="text" name="password" value="<?= old('password') ?>">
    </div>
    <div>
        <input type="submit" value="Login">
    </div>
    </form> 


Question: How can I redirect to back, with input data AND with the validation errors so I can display them in the form view?

OK, guys. Just to notice that I've found the solution. Well, I've made my study and get this. Don't know if it is the best one, but here it goes:

Controller (home):

PHP Code:

public function index()
{
    $data = [];
    if(session()->has('errors')){
        $data['error'] = session('error');
    }
    return view('form', $data);
}

public function afterPost()
{
    if ($this->request->getMethod() !== 'post') {
        return redirect()->to(site_url('home/index'));
    }

    // validation
    $val = $this->validate([
        'username' => 'required',
        'password' => 'required'
    ]);
    if (!$val) {
        return redirect()->to(site_url('home/index'))->withInput()->with('error', $this->validator);
    } else {
        echo 'Form is OK!';
    }
} 


View (form)

PHP Code:

<?php if (isset($error)) : ?>
        <?= $error->listErrors() ?>
<?php endif; ?>


<?= form_open('home/afterpost') ?>

    <div>
        <input type="text" name="username" value="<?= old('username') ?>">
    </div>
    <div>
        <input type="password" name="password" value="<?= old('password') ?>">
    </div>
    <div>
        <input type="submit" value="Login">
    </div>
</form>