keystone-classic: middleware (node-oauth2-server) can't return it's string

Hi, I am implementing oauth2 like I did in the expressjs project.

I put the following codes in routes/index.js

app.all('/oauth/token', oauth.grant());

It is triggered and token is generated in console.log.

in saveAccessToken (token: 4d82d4a819a6814459dde40e2e8f9d5f956d6028, clientId: myclientid, userId: 12345566666666, expires: Sun Feb 08 2015 11:15:51 GMT+0800 (HKT))

However, there is no return and Timeout.

In my expressjs, the oauth.grant() will return a token string. Is there anything I need to override in Keystonejs in order to let the middleware run the response?