function authenticate(name, pass, fn) {
    userOp.findOne({
        "username": name
    },

    function (err, user) {
        if (user) {
            if (err) return fn(new Error('cannot find user'));
            hash(pass, user.salt, function (err, hash) {
                if (err) return fn(err);
                if (hash == user.hash) return fn(null, user);
                fn(new Error('invalid password'));
            });
        } else {
            return fn(new Error('cannot find user'));
        }
    });
};
exports.login = function (req, res) {
  response = {};
  authenticate(req.body.username, req.body.password, function (err, user) {
      if (user) {
          req.session.regenerate(function () {
              req.session.user = user;
              req.session.success = user.username;
              res.redirect("/");
          });
      } else {
          req.session.error = 'Błąd autoryzacji. Sprawdz swój login lub hasło.';
          response = {"error": true, "message": req.session.error };
          res.json(response);
          }
  });
};