Twitter看起来api 401错误

Question

下面的代码帮助我用Twitter实现REST API调用

var oauth_token = membership.Token; //"insert here...";
                var oauth_token_secret = membership.TokenSecret; //"insert here...";
                var oauth_consumer_key = consumerKey;
                var oauth_consumer_secret = consumerSecret;

                // oauth implementation details
                var oauth_version = "1.0";
                var oauth_signature_method = "HMAC-SHA1";

                // unique request details
                var oauth_nonce = Convert.ToBase64String(
                    new ASCIIEncoding().GetBytes(DateTime.Now.Ticks.ToString()));
                var timeSpan = DateTime.UtcNow
                    - new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc);
                var oauth_timestamp = Convert.ToInt64(timeSpan.TotalSeconds).ToString();


                // create oauth signature
                var baseFormat = "oauth_consumer_key={0}&oauth_nonce={1}&oauth_signature_method={2}" +
                                "&oauth_timestamp={3}&oauth_token={4}&oauth_version={5}";

                var baseString = string.Format(baseFormat,
                                            oauth_consumer_key,
                                            oauth_nonce,
                                            oauth_signature_method,
                                            oauth_timestamp,
                                            oauth_token,
                                            oauth_version
                                            );

                baseString = string.Concat("GET&", Uri.EscapeDataString(resource_url), "&", Uri.EscapeDataString(baseString));

                var compositeKey = string.Concat(Uri.EscapeDataString(oauth_consumer_secret),
                                        "&", Uri.EscapeDataString(oauth_token_secret));

                string oauth_signature;
                using (HMACSHA1 hasher = new HMACSHA1(ASCIIEncoding.ASCII.GetBytes(compositeKey)))
                {
                    oauth_signature = Convert.ToBase64String(
                        hasher.ComputeHash(ASCIIEncoding.ASCII.GetBytes(baseString)));
                }

                // create the request header
                var headerFormat = "OAuth oauth_nonce=\"{0}\", oauth_signature_method=\"{1}\", " +
                                   "oauth_timestamp=\"{2}\", oauth_consumer_key=\"{3}\", " +
                                   "oauth_token=\"{4}\", oauth_signature=\"{5}\", " +
                                   "oauth_version=\"{6}\"";

                var authHeader = string.Format(headerFormat,
                                        Uri.EscapeDataString(oauth_nonce),
                                        Uri.EscapeDataString(oauth_signature_method),
                                        Uri.EscapeDataString(oauth_timestamp),
                                        Uri.EscapeDataString(oauth_consumer_key),
                                        Uri.EscapeDataString(oauth_token),
                                        Uri.EscapeDataString(oauth_signature),
                                        Uri.EscapeDataString(oauth_version)
                                );



                ServicePointManager.Expect100Continue = false;

                // make the request

                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(resource_url);
                request.Headers.Add("Authorization", authHeader);
                request.Method = "GET";
                request.ContentType = "application/x-www-form-urlencoded";
                var response = (HttpWebResponse)request.GetResponse();
                var reader = new StreamReader(response.GetResponseStream());
                var objText = reader.ReadToEnd();

                return objText.ToString();

但问题是，当我尝试实现https://api.twitter.com/1.1/statuses/lookup.json?id=20,432656548536401920 api时，它显示401错误。该错误仅来自此api调用。