HttpWebRequest 请求带OAuth2 授权的webapi

OAuth 2.0注意事项：
1、 获取access_token时，请使用POST

  private static string GetAuthorization(string username, string password)
         {
             string authorization = string.Format("{0}:{1}", username, password);

             return "Basic " + Convert.ToBase64String(new ASCIIEncoding().GetBytes(authorization));
         }

   /// <summary>
         /// 获取Token
         /// </summary>
         /// <returns></returns>
         private static string OAuthClientCredentialsToken()
         {
             const string clientId = "";
             const string clientSecret = "";
             string result = string.Empty;

             HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create(_baseUrl + "/token");
             httpWebRequest.Method = "POST";
             httpWebRequest.ContentType = "application/x-www-form-urlencoded";
             httpWebRequest.Accept = "application/json";
             httpWebRequest.Timeout = ;
             httpWebRequest.KeepAlive = false;
             httpWebRequest.AllowAutoRedirect = true;
             // httpWebRequest.Headers.Add("Accept-Language", "zh-cn");
             //  httpWebRequest.Headers.Add("Accept-Encoding", "gzip, deflate");
             // httpWebRequest.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.1.4322)";
             httpWebRequest.Headers.Add("Authorization", GetAuthorization(clientId, clientSecret));
             //Credentials
             httpWebRequest.Credentials = CredentialCache.DefaultCredentials;
             //post参数
             StringBuilder postParam = new StringBuilder();
             Dictionary<string, string> parameters = new Dictionary<string, string> { { "grant_type", "client_credentials" } };
             int i = ;
             foreach (KeyValuePair<string, string> parameter in parameters)
             {
                 if (i > )
                     postParam.Append("&");
                 postParam.AppendFormat("{0}={1}", parameter.Key, HttpUtility.UrlEncode(parameter.Value));
                 i++;
             }

             byte[] postData = Encoding.UTF8.GetBytes(postParam.ToString());
             httpWebRequest.ContentLength = postData.Length;

             try
             {
                 Stream requesStream = httpWebRequest.GetRequestStream();
                 requesStream.Write(postData, , postData.Length);
                 requesStream.Close();

                 WebResponse response = httpWebRequest.GetResponse();
                 Stream stream = response.GetResponseStream();
                 if (stream != null)
                 {
                     using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
                     {
                         result = reader.ReadToEnd();
                         reader.Close();
                     }
                     stream.Close();
                 }
             }
             catch (WebException ex)
             {
                 throw new Exception(ex.Message);
             }
             return !string.IsNullOrWhiteSpace(result) ? JObject.Parse(result)["access_token"].Value<string>() : result;
         }

2、 访问需要授权的Api，请使用http/https协议，并且加上access token的Header
3 、Header格式为"Authorization: Bearer access_token"，其中Bearer后面有一个空格

  /// <summary>
         /// HttpGet
         /// </summary>
         /// <param name="url"></param>
         /// <param name="token"></param>
         /// <param name="contentType"></param>
         /// <returns></returns>
         private static string HttpGet(string url, string token, string contentType = "application/x-www-form-urlencoded")
         {
             HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
             httpWebRequest.Method = "GET";
             httpWebRequest.ContentType = contentType;
             httpWebRequest.Accept = "application/json";
             httpWebRequest.Timeout = ;
             httpWebRequest.AllowAutoRedirect = false;
             //Bearer+空格
             httpWebRequest.Headers.Add("Authorization", "Bearer " + token);
             httpWebRequest.Credentials = CredentialCache.DefaultCredentials;

             string result = null;
             try
             {
                 WebResponse response = httpWebRequest.GetResponse();
                 Stream responseStream = response.GetResponseStream();
                 if (responseStream != null)
                 {
                     using (StreamReader streamReader = new StreamReader(responseStream, Encoding.UTF8))
                     {
                         result = streamReader.ReadToEnd();
                         streamReader.Close();
                     }
                 }
             }
             catch (Exception ex)
             {
                 throw new Exception(ex.Message);
             }
             return result;
         }