I am trying  for the Oauth  Code.It is Working fine with linkedin oauth api but  when i try with the salesforce it throws an error 'Signature invalid'. I tried with the get and post methods but not able to resolve this methods.can anyone any idea about  how to get the request token.

string stroauth_signature_method = "HMAC-SHA1";

            string stroauth_version = "1.0";

            string outUrl = "";

            string querystring = "";

            string consumerKey = "3MVG9Y6d_Btp4xp5HE.zoyjqpLRQO7n9twJD9LCyT6DAfnpxkv5EmtHIaxkM5duimUltRtubV8Aa4OexNatwT";

            string consumerSecret = "1964943390161656075";

            //Uri uri = new Uri(@"https://api.linkedin.com/uas/oauth/requestToken");

            Uri uri = new Uri(@"https://login.salesforce.com/_nc_external/system/security/oauth/RequestTokenHandler");

            Uri uri1 = new Uri(@"https://login.salesforce.com");

            OAuthBase oAuth = new OAuthBase();

            string nonce = oAuth.GenerateNonce();

            string timeStamp = oAuth.GenerateTimeStamp();

            string sig = oAuth.GenerateSignature(uri, consumerKey, consumerSecret, string.Empty, string.Empty, "POST", timeStamp, nonce,OAuth.OAuthBase.SignatureTypes.HMACSHA1, out outUrl, out querystring);

            sig = HttpUtility.UrlEncode(sig);

            StringBuilder sb = new StringBuilder();

            sb.AppendFormat("oauth_consumer_key={0}", consumerKey);

            sb.AppendFormat("&oauth_nonce={0}", nonce);

            sb.AppendFormat("&oauth_signature_method={0}", stroauth_signature_method);

            sb.AppendFormat("&oauth_signature={0}", sig);

            sb.AppendFormat("&oauth_timestamp={0}", timeStamp);          

            sb.AppendFormat("&oauth_version={0}", stroauth_version);           

            sb.AppendFormat("&oauth_callback={0}", "oob");

            //uri = new Uri(sb.ToString());

            //sb.AppendFormat("&oauth_token={0}", "11111111");

            HttpWebRequest request = System.Net.WebRequest.Create(uri.ToString()) as HttpWebRequest;

            //HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri.ToString());

            request.Method = "POST";

            request.ContentType = "application/x-www-form-urlencoded";

            //request.Headers.Add("oauth_consumer_key", consumerKey);

            //request.Headers.Add("oauth_nonce", nonce);

            //request.Headers.Add("oauth_timestamp", timeStamp);

            //request.Headers.Add("oauth_signature_method", stroauth_signature_method);

            //request.Headers.Add("oauth_version", stroauth_version);

            //request.Headers.Add("oauth_signature", sig);

            //request.Headers.Add("oauth_callback", "oob");

            request.Headers.Add("Authorization", "OAuth oauth_consumer_key=\"" + consumerKey + "\",oauth_signature_method=\"HMAC-SHA1\",oauth_signature=\"" + sig + "\",oauth_timestamp=\"" + "1191242096" + "\",oauth_nonce=\"" + nonce + "\", oauth_version=\"1.0\",oauth_callback=\"oob\"");

            //request.Credentials = CredentialCache.DefaultCredentials;

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            //using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)

            //{

            //    using (TextReader reader = new StreamReader(response.GetResponseStream()))

            //    {

            //        ///oauthtokendata = HttpUtility.ParseQueryString(reader.ReadToEnd());

            //    }

            //}