PHO POO chapitre 20 - Back-end - Undefined array key "username"

Bonjour,

L'affichage du formulaire dans la page "index.php?p=login fonctionne. Mais quand je soumets le formulaire login.php, j'obtiens des warnings : undefined array key "usernames" et undefined array key "passwords". Or, le var_dump($POST) affiche :
array(2) { ["username"]=> string(4) "demo" ["password_"]=> string(4) "demo" }

Ci-dessus le fichier Login.php :

<?php

use Core\Auth\DBAuth;
use Core\HTML\BootstrapForm;

$form = new BootstrapForm($_POST);

if(!empty($_POST)) {
    $auth = new DBAuth(App::getInstance()->getDb());
    var_dump($_POST);
    if($auth->login($_POST["username"], $_POST["password"])) {
        die('Connecté');
    }
    else {
        die('Non connecté');
    }
}

//$form = new BootstrapForm($_POST);

?>

<form method = "POST" style="margin-top: 20px;">
    <?= $form->input('username', 'Pseudo'); ?>
    <?= $form->input('password', 'Mot de passe', ['type' => 'password']); ?>
    <?= $form->submit() ?>
</form>

et la classe DBAuth :

<?php

namespace Core\Auth;

use Core\Database\Database;

class DBAuth {

    private $db;

    public function __construct(Database $db) {
        $this->db = $db;
    }

    /**
     * @param $username
     * @param $password
     * return boolean
     */
    public function login($username, $password) {
        $user = $this->db->prepare(
            "SELECT * FROM users WHERE username = ?", 
            [$username], 
            null, 
            true
        );
        if($user) {
            return $user->password = sha1($password);
        }
        else {
            return false;
        }
    }

    public function logged() {
        return isset($_SESSION['auth']);
    }

}

?>

Ce que j'obtiens

aarray(2) { ["username"]=> string(4) "demo" ["password"]=> string(4) "demo" }

Warning: Undefined array key "username" in C:\xampp\htdocs\www\POO\Blog\pages\users\login.php on line 11

Warning: Undefined array key "password" in C:\xampp\htdocs\www\POO\Blog\pages\users\login.php on line 11

Non connecté