public async Task <IActionResult> MarkDone(Guid id)
        {
            if (id == Guid.Empty)
            {
                return(RedirectToAction("Index"));
            }

            var currentUser = await _userManager.GetUserAsync(User);

            if (currentUser == null)
            {
                return(RedirectToAction("Index"));
            }

            var successful = await _toDoListTaskService.MarkDoneAsync(id, currentUser);

            if (!successful)
            {
                return(BadRequest("Could not mark task as done."));
            }

            return(RedirectToAction("Index"));
        }