I use Express and socket.io.

When you create a session with the express - post. Click the button and using Ajax and the POST method (login), I save a session.

 app.post('/login', function(req, res){
         req.session.loginid = req.body.lgnid;
    });

In socket.io it can not read.

Thanks for the advice.

My source code.:

var express = require('express');
var app = express.createServer();
var io = require('socket.io').listen(app); 
var MemoryStore = express.session.MemoryStore;
var sessionStore = new MemoryStore();
var parseCookie = require('connect').utils.parseCookie;
var Session = require('connect').middleware.session.Session;
var stylus = require('stylus');
  app.use(express.bodyParser());
  app.use(express.cookieParser());
  app.use(express.session({store: sessionStore
        , secret: 'secret'
        , key: 'express.sid'}));

  app.use(stylus.middleware({ src: __dirname + '/public', compile: compile }))
  app.use(express.static(__dirname + '/public'));
  app.set('views', __dirname);

 // disable layout
  app.set("view options", {layout: false});

  // make a custom html template
  app.register('.html', {
    compile: function(str, options){
      return function(locals){
        return str;
      };
    }
  });

  function compile (str, path) {
    return stylus(str)
      .set('filename', path)
      .use(nib());
  };

var Session = require('connect').middleware.session.Session;
sio.set('authorization', function (data, accept) {
    if (data.headers.cookie) {
        data.cookie = parseCookie(data.headers.cookie);
        data.sessionID = data.cookie['express.sid'];
        // save the session store to the data object 
        // (as required by the Session constructor)
        data.sessionStore = sessionStore;
        sessionStore.get(data.sessionID, function (err, session) {
            if (err || !session) {
                accept('Error', false);
            } else {
                // create a session object, passing data as request and our
                // just acquired session data
                data.session = new Session(data, session);
                accept(null, true);
            }
        });
    } else {
       return accept('No cookie transmitted.', false);
    }
});

How to load and save data from sessionStore?

io.sockets.on('connection', function (socket) {

    var hs = socket.handshake;
    console.log('Session : ' + hs.session.loginid + '); //Session : undefined

});

A recommended way to achieve this actually (at least in my experience) is to forgo the sessionStore.get function and go for sessionStore.load instead - the difference is that with load the callback is given a session instance instead of having to create one yourself. The difference is simply taking your snippet:

sessionStore.get(data.sessionID, function (err, session) {
    if (err || !session) {
        accept('Error', false);
    } else {
        // create a session object, passing data as request and our
        // just acquired session data
        data.session = new Session(data, session);
        accept(null, true);
    }
});

And changing it to:

sessionStore.load(data.sessionID, function(err, session) {
  if (err || !session) {
    accept("Error", false);
  } else {
    data.session = session;
    accept(null, true);
  }
});

And from there, you should be able to access the session as you attempt, such as socket.handshake.session, however when dealing with the session if you make changes in a socket event you have to manually save the session yourself. If you add/remove things you must: session.save([callback]).

I realize this isn't much of an answer since I'm telling you to do roughly what you already are but this is working for me right now with Express 2.5.8 and Socket.IO 0.9.6.