def METHOD_NAME(self, app: Quart, session: SessionMixin) -> datetime | None:
    """Helper method to return the Session expiration time.
    If the session is not 'permanent' it will expire as and when
    the browser stops accessing the app.
    """
    if session.permanent:
        return datetime.utcnow() + app.permanent_session_lifetime
    else:
        return None