public function autheticate($username, $password)
    {

        $query = "SELECT U.username, U.password FROM users as U WHERE U.username = ? AND U.password = ?";

        if($stmt = $this->conn->prepare($this->conn, $query))
        {
            $stmt->bind('ss',$username, $password);

            $stmt->execute();

            $stmt->close();

            return true;
        }

     // print_r($this->conn);
    }

mysqli Object
(
    [affected_rows] =>
    [client_info] =>
    [client_version] => 50547
    [connect_errno] => 0
    [connect_error] =>
    [errno] =>
    [error] =>
    [error_list] =>
    [field_count] =>
    [host_info] =>
    [info] =>
    [insert_id] =>
    [server_info] =>
    [server_version] =>
    [stat] =>
    [sqlstate] =>
    [protocol_version] =>
    [thread_id] =>
    [warning_count] =>
)