but each time user request the server, the session store(like redis) will reset expire time. and if we don't update cookie's max age or expires, it may cause some problems?

in `connect.session`, it will reset cookie when session modified. https://github.com/senchalabs/connect/blob/master/lib/middleware/session.js#L250

i'm not fully understand why only set cookie when session modified. it seems like also no need to reset session in store when session not modified.