public function getUserInfo(){
            $stmt = $this->dbh->prepare("SELECT user_id FROM oopforum_users WHERE username = ?");
            $stmt->bindParam(1, $this->post_data['username']);
            $stmt->execute();

            while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {

                $password = $row['password'];
                $user_id = $row['user_id'];
                $img_thumb = $row['thumbnail'];
            }
            return array(
                'password' => $password,
                'id' => $user_id,
                'thumb' => $img_thumb

                );

        }

// CALLING CODE BELOW

session_start();
require_once('init.php');

$username = trim($_POST['username']);
// create a new object
$login = new Auth($_POST, $dbh);

    if($login->validateLogin()){

        $_SESSION['loggedin'] = true;
        $list = $login->getUserInfo();
        $_SESSION['password'] = $list['password'];
        $_SESSION['id'] = $list['id'];
        $_SESSION['thumb'] = $list['thumb'];
}

print_r($_SESSION);