request.session undefined . nodeJS express

there were many questions about this topic around , but none could solve my problem , i developed an express app and my authentication method was to write to session object and using redis-store . it worked perfect during development ,

but the first time i deployed my site for some tests ( using modulus ) i get an error that req.session is undefined . the code still works fine when i run this on localhost .

this is actually my first web project and there were so many obvious points and tricks that i didn't know and had to learn through the way . maybe i'm missing something simple and obvious here , don't know !

package.josn dependencies :

  "dependencies" : {
        "express"    : "~3.4.4",
        "mongoose"   : "~3.6.2",
          "socket.io":"1.x" ,
        "bcrypt-nodejs" : "0.0.3",
        "connect-redis": "1.4.x" ,
        "body-parser" : "1.4.3" ,
        "cookie-parser": "~1.0.0",
        "express-session": "~1.0.0"
    } ,   

app configuration

var express = require('express') ;
var app = express() ;
var http = require('http') ;
var io = require('socket.io') ;
var bodyParser   = require('body-parser');
var mongoose = require('mongoose') ;
var mongoose1 = require('mongoose') ;
var bcrypt = require('bcrypt-nodejs') ;
var PORT = process.env.PORT || 8080 ;
var server = http.createServer(app) ;
var RedisStore = require('connect-redis')(express);

app.configure(function () {
    app.use(express.static(__dirname + "/static" )) ;
    app.use( express.cookieParser() );
    app.use(express.bodyParser()) ;
    app.use(express.session({
        store: new RedisStore({
            host: 'localhost',
            port: 6379,
            db: 2,
            pass: '****'
        }),
        secret: '12345qwr'
    })
    );

}) ;

and when i reach req.session.[] in my server , app crashed and restarts because req.session in undefined . for example when I click on a login button and a post request is sent to "/api/login" or ..

    app.post('/api/login' , function (req, res) {
        UserDBModel.findOne({ username : req.body.user } , function (err, user) {
            if (err) { res.json(err) ; }
            if ( user ) {
                if ( bcrypt.compareSync( req.body.pass ,  user.password ) ) {
                    req.session.Auth = { username : user.username , password : user.password } ;
//app crashes here with error : TypeError: Cannot set property 'Auth' of undefined

    }) ;

ps. to authenticate , i store an "Auth" object in my session containing username and hashed password of logged in users .