Node js + express + session

I was figuring out how to create a session after somebody logs in. I would like to have a function that creates the session, a function to check if a session is active(if somebody loged in) and a way to close it.

I searched a lot but nothing seemed to work, probably it's my error. Here is my code so far.

    var   express   = require('express')
    , exp       = express()
    , fs        = require('fs')
    , pub       = 'public/'
    , port      = 80
    , log       = fs.createWriteStream('./web.log', {flags: 'w'});;

exp.configure(function(){
    exp.use(express.static(__dirname + '/' + pub));
    exp.use(express.logger({stream: log})); 
    exp.use(express.bodyParser());
    exp.use(express.cookieParser());
    exp.use(express.session({secret:'sea-anemone'}));
});

exp.get('/', function(req, res){
    res.sendfile(pub + 'index.html');
});

exp.post('/', function(req, res){
    var u = req.param('username', null);
    var p = req.param('password', null);
    If (u == "admin" && p == "pass"){
        /* call function to create session */
    }
});

console.log("Server started")
exp.listen(port);