Why is there set-cookie in every response?
Even though there is a cookie in the request, there is a set-cookie in each response. 
Why not only set-cookie in the first response?
Thank you；
this my koa-session config:

<img width="427" alt="截屏2021-08-25 19 09 14" src="https://user-images.githubusercontent.com/45303288/130780292-93df26b8-ffed-4ddc-a5cf-00f3ba5e628d.png">