What is the equivalent to Express's `app.locals`
I'm trying to pass the session to the jade templates so I can check things e.g. authentication, userlevel, so on so forth, but I can't for the life of me figure out how to pass it to `locals` from a middleware, e.g. in my express 4 app:

```
app.use((req, res, next) => {
   app.locals.req = req;
   next();
});
```

now in Koa2

```
app.use(async (ctx, next) => {
    try {
        console.log(ctx.req.locals);
        console.log(ctx.req.state);
                console.log(ctx.state);
                console.log(ctx);
        ctx.state.session = ctx.session;
        await next();
    } catch(err) {
        ctx.body = { message: err.message };
        ctx.status = err.status || 500;
    };
});
```
