angular.sample.authService.js

angular.module('app', [])
    .config(function($routeProvider) {
        $routeProvider.when('/needsauth', {
            // config for controller and view
            resolve: {
                'auth': function(AuthService) {
                    return AuthService.authenticate();
                }
            }
        });        
    })
    .factory('AuthService', function($q) {
        function _authenticate() {
            var isAuthenticated;
            
            // authentication logic
            if(isAuthenticated) {
                return true;
            } else {
                return $q.reject('Not Authenticated');
            }
        };
    })
    .run(function($rootScope, $location) {
        $rootScope.$on('$routeChangeError', function(current, previous, rejection) {
            if(rejection === 'Not Authenticated') {
                $location.path('/login');
            }
        });
    });