node7,koa2,koa-session2写cookie失败，操作cookie需要用哪个中间件吗，客户端angular2

const Koa = require('koa');
const session = require("koa-session2");
const Store = require("./Store.js");
const app = new Koa();
app.use(session({
    key: "SESSIONID",   //default "koa:sess"
    //store: new Store()
}));
app.use(async (ctx, next) => {
  ctx.session.user = 'aaa';
  ctx.cookies.set("SESSIONID", 'sdfwfswed', {key: "SESSIONID"});
  ctx.cookies.get("SESSIONID", {key: "SESSIONID"});//undefined
});

无论是设置session键值还是手工设置cookie，都失败，客户端下次请求cookie一直为空 DX帮忙看看，谢谢