public async Task <IActionResult> CreateUser(CreateUserViewModel user)
        {
            if (!ModelState.IsValid)
            {
                return(UnprocessableEntity());
            }

            var createdUser = await _dataStore.CreateUserAsync(user.UserName, user.Password).ConfigureAwait(false);

            if (createdUser == null)
            {
                return(Conflict());
            }

            return(Ok(createdUser));
        }