function requireUser(req, res, next){
//console.log(req.session.username);
 if (!req.session.username) {
   res.redirect('/user_unauthorized');
  }
 else{
   next();
  }
}

app.get('/dashboard', requireUser, function(req, res){
  res.sendFile('dashboard.html',{root: path.join(__dirname,'./')});
});

function authenticateUser(username, password, callback){
 var coll = mongo.collection('users');

 coll.find({username: username, password:password}).toArray(function(err, user){
 console.log(user);
 callback(err, user);
 });
}

app.post('/login', function(req, res){
var username = req.body.username;
var password = req.body.password;

 authenticateUser(username, password, function(err, user){
  if (user.length) {
    // This way subsequent requests will know the user is logged in.
    req.session.username = user[0].username;
    console.log(req.session.username);
    res.redirect('/dashboard');
  } else {
    console.log('user not authenticated');
    res.redirect('/invalid_credentials');
  }
 });
});