How to detect multiple socket.io connections from same user

I have followed this guide: http://www.danielbaulig.de/socket-ioexpress/ to link express.js to socket.io and it works brilliantly.

I have the user logging in on one page (express.js POST request that sets a session object) and when they have authenticated it directs them to a new page where socket.io loads and on the server socket.io can grab the session that was set from express. So that all works fine.

Now I have users on the page that uses socket.io and when that page is refreshed - sometimes the socket.io connection is still there (ie. it doesn't disconnect). What I am trying to do is alter the io.set('authorization') function to ensure that when the user connects - it will disconnect all existing socket.io instances that are still open to that client.

Here is the how it looks at the moment:

//socket.io connect to express
var parseCookie = require('connect').utils.parseCookie;
io.set('authorization', function (data, accept) {
    if (data.headers.cookie) 
    {
        data.cookie = parseCookie(data.headers.cookie);
        data.sessionID = data.cookie['express.sid'];
        // (literally) get the session data from the session store
        sessionStore.get(data.sessionID, function (err, session) 
        {
            if (err || !session) 
            {
                // if we cannot grab a session, turn down the connection
                //note: a session is created when the user logs in
                accept('Error', false);
            } 
            else 
            {
                //TODO something here before we accept the connection
                //??

                // save the session data
                data.session = session;
                //accept the connection
                accept(null, true);
            }
        });
    } 
    else 
    {
        return accept('No cookie transmitted.', false);
    }
});

How do I check if the client that is about to be accepted has a previous connection, and it is still open (and therefore we need to disconnect that old one).

The express session has a "username" in it - so we can get the session object and get the username, I just can't figure out how to go through the list of all the socket.io clients and have a look at the express session for each one and check if it the same as the user authenticating currently.