public string GetRequestTokenAuthorizeUrl(string userId)
        {
            var requestToken = GetRequestToken(_consumer);

            requestToken.UserId = userId;

            var existingToken = _requestTokenStore.Find(userId);

            if (existingToken != null)
            {
                _requestTokenStore.Delete(requestToken);
            }

            _requestTokenStore.Add(requestToken);

            return(GetAuthorizeUrl(requestToken));
        }