How to use Promises for the win

AuthenticationServices.js

angular.module('myapp.security')
	.factory('authentication', function ($http, $q, settings, authService) {
		this._userContext = null;
		var _this = this,
			_fetchContext = function () {
				var deferred = $q.defer();
				$http({
					method: 'GET',
					url: settings.authentication.resourceEndPoints.context
				})
				.success(function (userContext) {
					if (userContext) {
						_this._userContext = userContext;
						deferred.resolve(userContext);
					}
					deferred.reject(new Error('Load user context response was empty'));
				})
				.error(function (data, status) {
					deferred.reject(new Error('Error thrown by $http when trying to load user context', data, status));
				});

				return deferred.promise;
			},
			_hasContext = function () {
				return _this._userContext != null;
			},
			_authenticate = function (username, password) {
				var deferred = $q.defer();
				$http({
					method: "POST",
					url: settings.authentication.resourceEndPoints.login,
					data: $.param({
						j_username: username,
						j_password: password
					})
				})
					.success(function (data) {

						if (data === "") {
							deferred.reject("Response data was empty.");
							return;
						}

						_this._userContext = data;

						authService.loginConfirmed(_this._userContext);

						deferred.resolve(data);
					})
					.error(function () {
						deferred.reject(new Error('Error thrown by $http when calling login.'));
					});
				return deferred.promise;
			},
			_logout = function () {
				var deferred = $q.defer();

				$http({
					method: 'GET',
					url: settings.authentication.resourceEndPoints.logout
				})
					.success(function () {
						deferred.resolve(true);
					})
					.error(function () {
						deferred.reject(new Error("Could not logout user."));
					});

				return deferred.promise;
			};


		return {
			fetchContext: _fetchContext,
			authenticate: _authenticate,
			hasContext: _hasContext,
			logout: _logout
		};
	});

simplified.js

angular.module('myapp.myservicemodule')
	.factory('myservice', function ($http, $q, settings, authService) {
		this._userContext = null;
		var self = this			
			_get = function () {
				var deferred = $q.defer();
				$http({
					method: "GET",
					url: settings.myservice.resourceEndPoints.url
				})
				.success(function (data) {

						if (data === "") {
							deferred.reject("Response data was empty.");
							return;
						}

						self._userContext = data;

						deferred.resolve(data);
					})
					.error(function () {
						deferred.reject(new Error('Error thrown by $http when calling login.'));
					});
				return deferred.promise;
			};


		return {
			get: _get
		};
	});