Apart from the API routes, we use express middleware for Server Side Rendering of react components. You can find the code here.
As @saiki explained, SailsJs is a wrapper around the express js. As I understood from SailsJs documentation, you can still use express middlewares in SailsJs. You just have to put the above mentioned code in sails.config.http.middleware file. If you run into any issues doing that, let me know.