with koa-session2
Hi,

I'm trying to use this with koa-session2 since both support v2.x.  The ctx.isAuthenticated() is never true 

```
// Require authentication for now
app.use(function (ctx, next) {
  console.dir('url: '+ctx.originalUrl+' auth?: '+ctx.isAuthenticated());     //ctx.isAuthenticated() never true
  if (!ctx.originalUrl.startsWith("/b2b/") || ctx.isAuthenticated()) {
    return next();
  } else {
    ctx.redirect('/');
  }
});

```

I do see the user and password work.  Most of the code I'm testing is based on the https://github.com/mapmeld/koa-passport-example mongo example.

This example runs for me on nodejs 6.2.0.  Is there any example or test with koa-session2?
