How to access session in express, outside of the req?

I know that I can use

function(req, res) {
    req.session
}

using express. However I need to access the session outside of the response function. How would I go about doing that?

I'm using socket.io to pass information for adding posts and comments. So when I receive the socket.io message on the server-side, I need to verify the person posting the information by using the session. However since this is being done via socket.io there is no req/res.