public async Task <IHttpActionResult> DeleteClient(Guid id)
        {
            var client = _refreshTokenManager.FindClient(id);

            if (client == null)
            {
                return(NotFound());
            }
            var result = await _refreshTokenManager.RemoveClient(id);

            if (result)
            {
                return(Ok());
            }
            ModelState.AddModelError("", $"Client: '{id}' could not delete.");

            return(BadRequest(ModelState));
        }