Ah OK, didn't realise you were working from the extendApp example. The ma-connection, ma-username, ma-password only work in conjunction with the default dashboard boostrapping file aka require(['mango-3.0/bootstrap']). If you are working from extendApp you are bootstrapping the application yourself, so you don't need to include the require(['mango-3.0/bootstrap']) line.
What you do need to do is add some code to extendApp.js that logs your user in before bootstrapping the application. Change the last part of the file from
angular.element(document).ready(function() {
angular.bootstrap(document.documentElement, ['myApp']);
});
To
var injector = angular.injector(['myApp']);
var User = injector.get('User');
User.login({
username: 'user',
password: 'password',
logout: true
}).$promise.then(function() {
angular.element(document).ready(function() {
angular.bootstrap(document.documentElement, ['myApp']);
});
});