AngularJS - Google logout directive

Our application needed a function to sign out of Google. Unfortunately, there is no such API and I was forced to use an iframe to: http://accounts.google.com/Logout and a polling mechanism to see when the operation is complete.

I had a lot of doubts whether to put this code in a directive or in a service.

On one hand it has DOM manipulation, so the instinct is to put it in a directive.

On the other hand:

• The directive is completely invisible. Most of the time it doesn't create any DOM, and only during logout it creates a hidden iframe.
• The usage of this directive, isn't by invoking an event in event in its template, since, as I said, it is invisible. The logout logic will be invoked in a logic in a controller/service so I will be basically calling a function inside the directive.

I would appreciate a code review regarding this points, and of course, anything else that comes to your mind:

// This directive allows a controller to log-out easily from Google
// Usage:
// <tg-google-logout logout-control="googleLogoutControl"></tg-google-logout>
// The given parameter must be an object. This object, is assigned by a directive by a single "logout" function.
// When logout is needed, it can be invoked using this object, e.g in this case in the controller you would write:
//  $scope.googleLogoutControl.logout()
// This function returns a promise. This promise gets resolved if logout was successful and rejected otherwise.
// If the user isn't logged out in MAX_LOGOUT_TIME_SECONDS
angular.module('codereview').directive('tgGoogleLogout', function () {
    'use strict';

    return {
        restrict: 'E',
        replace: true,
        template: '<iframe class="hidden" ng-if="showLogoutFrame" src="https://www.google.com/accounts/Logout"></iframe>',
        scope: {
            logoutControl: "="
        },
        controller: function ($scope, $q, $timeout, $log, googleAuthService) {

            var MAX_LOGOUT_TIME_SECONDS = 5;

            $scope.showLogoutFrame = false;

            // Polls Google until user is completely logged out
            // maxSecondsToWait - The maximum number of seconds for a logout to happen.
            // Returns a promise. Resolves when logout is detected. Rejects if logout was not detected in time.
            function waitUntilLogout(maxSecondsToWait) {
                // Default - Time to try before giving up on logout
                if (angular.isUndefined(maxSecondsToWait)) {
                    maxSecondsToWait = 5;
                }

                return googleAuthService.getAuthorizedUserEmail()
                    .then(function (email) {
                        $log.debug("getAuthorizedUserEmail - Got email: {0}".format(email));
                        if (email) {
                            maxSecondsToWait--;

                            if (maxSecondsToWait > 0) {
                                // Retry after 1000ms. The actual function happens on the next "then".
                                // NOTE: The total amount of seconds we will retry, is set by 'maxSecondsToLogout'
                                //       This controls only how often we try.
                                $log.debug("getAuthorizedUserEmail - Retrying {0} seconds left".format(maxSecondsToWait));

                                return $timeout(function () {
                                }, 1000).then(function () {
                                    return waitUntilLogout(maxSecondsToWait)
                                });
                            } else {
                                return $q.reject("Failed to logout");
                            }
                        }
                    });
            }

            if (!angular.isObject($scope.logoutControl)) {
                throw new Error("logoutControl - A control object is required to use this directive. It can be an empty object.")
            }

            if (angular.isDefined($scope.logoutControl.logout)) {
                throw new Error("logoutControl - logout property must not be already defined - Overwrite risk")
            }

            // See directive docs for usage.
            //noinspection JSPrimitiveTypeWrapperUsage
            $scope.logoutControl.logout = function () {
                // Showing the frame starts the logout process
                $scope.showLogoutFrame = true;

                return waitUntilLogout(MAX_LOGOUT_TIME_SECONDS)
                    .finally(function () {
                        // Hide the frame regardless of success/failure of logout
                        $scope.showLogoutFrame = false;
                    });
            }
        }
    };
});