How check a users name when accessing a route

Hi guys ive spent the last 3 hours trying to get this work so any help would be greatly appreciated. So i made an express webapp that has an admin page. I have the register and login done using passport and i can check if the user is logged in with the function

var isAuthenticated = function (req, res, next) {
// if user is authenticated in the session, call the next() to call the next request handler 
// Passport adds this method to request object. A middleware is allowed to add properties to
// request and response objects
if (req.isAuthenticated())
    return next();
// if the user is not authenticated then redirect him to the login page
res.redirect('/');}

I when i click on the link for my admin route i want to check to see if the users username is equal to example and if it is allow it into the page. My code so far is

  var isAdmin = function (req, res, next) {

  var post = req.body;
    if (post.username === 'example') {

    return next();
  }else{
  // if the user is not authenticated then redirect him to the login page
  res.redirect('/');
}

and my route is

router.get('/admin', isAdmin, function(req, res){
    res.render('admin', { title : 'admin' });
});

I have both of these code snipets in my index route file. The problem that i am getting is that when i try to log in with the user called example it returns me to the login page. Any ideas how to fix?