public function doLogin($username,$password)
    {
        $hash = password_hash($password, PASSWORD_DEFAULT);
        $stmt = $this->mysqli->prepare("SELECT id FROM utenti WHERE username = ? AND password = ? ");
        $stmt->bind_param("ss",$username,$hash);
        $stmt->execute();

        $stmt->bind_result($id);
        $stmt->store_result();

        if($stmt->num_rows)
        {
            throw new Exception("Utente trovato");
        }
        throw new Exception("Utente o password errati!");
    }