can not get ctx.session
i want to design a signin/signup system ,and i set some information in ctx.session like example in an api like xxx/signin,but when i want to signup ,i can not get the ctx.session .PS:option is same as example
here is my environment:  

> "node": "8.9.3"
> "koa": "^2.2.0",
> "koa-session": "^5.0.0"

thank you  for you reply!