Ionic client to the API with NodeJS

I have a problem, it's an API with NodeJS and the client with Ionic (code available here as well).

// SERVICES.JS
angular.module('app.services', [])

.factory('loginService', function($http){
    return{
        print: function() {
            return $http.get('http://EXTERNALURL:3000/print').then(function(res) {
                return res.data;
            })
        },
        login: function(post) {
            return $http({
                url: 'http://EXTERNALURL:3000/login',
                method: 'POST',
                data: post,
                headers: {'Content-Type': 'application/x-www-form-urlencoded'}
            }).success(function (data, status, headers, config) {
                console.log(data);
            }).error(function (data, status, headers, config) {
                console.log(status);
            });
        }
    }
})
// ROUTES.JS en servidor externo 
app.post('/login', function(req, res){
    console.log(req.body)
    AM.manualLogin(req.body['user'], req.body['pass'], function(e, o){
        if (!o){
            res.status(400).send(e);
        }   else{
            req.session.user = o;
            if (req.body['remember-me'] == 'true'){
                res.cookie('user', o.user, { maxAge: 900000 });
                res.cookie('pass', o.pass, { maxAge: 900000 });
            }
            res.status(200).send(o);
        }
    });
});

The problem is that when sending the data from postman on the server by the line console.log(req.body) shows them to me like this:

{"user":"[email protected]","pass":"Seighei7"}

Which is the correct way, but when sending them from Ionic with the client that armes in services.js it shows it like this:

{ '{"user":"[email protected]","pass":"Seighei7"}': '' }