Problems with C# HTTP Post with Authentication

I'm trying to send some XML through HTTP Post. But I'm getting 401 Unauthorized. Funny thing is when I access the URL through the browser, the username/password I provide are OK.

Here is my method signature:

        internal static string Send(string URL, string XMLdata, string RequestMethod, 
                                    string RequestUsername, string RequestPassword)

I have tried this as method body:

        string requestData = XMLdata;
        string responseData = "";

        StreamWriter myWriter = null;
        HttpWebRequest objRequest = (HttpWebRequest)WebRequest.Create(URL);

        objRequest.Method = RequestMethod;
        objRequest.PreAuthenticate = true;
        objRequest.ContentType = "application/x-www-form-urlencoded";//"text/xml";
        objRequest.Credentials = new NetworkCredential(RequestUsername, RequestPassword);;
        objRequest.ContentLength = requestData.Length;

        try
        {
            myWriter = new StreamWriter(objRequest.GetRequestStream());
            myWriter.Write(requestData);
        }
        finally
        {
            myWriter.Close();
        }

        StreamReader sr = null;

        try
        {
            HttpWebResponse objResponse = (HttpWebResponse)objRequest.GetResponse();
            sr = new StreamReader(objResponse.GetResponseStream());
            responseData = sr.ReadToEnd();
        }
        finally
        {
            if (sr != null)
                sr.Close();
        }

        return responseData;

And also this:

        string result;

        using (var client = new WebClient())
        {
            Uri requestUri = new Uri(URL);
            CredentialCache cache = new CredentialCache();
            NetworkCredential nc = new NetworkCredential(RequestUsername, RequestPassword);
            cache.Add(requestUri, "Basic", nc);
            client.Credentials = cache;

            result = client.UploadString(requestUri, XMLdata);
        }

        return result;

Both get the 401. What am I doing wrong? Just a reminder: when I access the URL through the browser, it prompts for username/password and the credentials I provide are OK.

My readings on the subject so far:

• HttpClient and forms authentication in C#
• Login to th开发者_StackOverflow中文版e page with HttpWebRequest
• HTTP POST Returns Error: 417 "Expectation Failed."
• HTTP Post XML document - server receives only first line
• POST to HTTPS authentication error
• C# Xml in Http Post Request Message Body

I appreciate the help.

[At request of OP, I'm migrating my comment to an answer]

I don't have an answer for you, from your description, but I do have a suggestion: use Fiddler to see what the request and response look like, both when the browser request succeeds, and when the programmatic request fails. I suspect there will be a difference that jumps out at you.

I solved it. Actually I was misled by the provider to make a mistake with the URL. The reason I'm posting my answer is for future reference, if someone ever comes across this.

The provider emailed me with the URL http://api.providersurl.com. When I get that into browser, it gets redirected to https://api.providersurl.com (HTTPS!). Then, I'm able to authorize with the credentials.

The funny thing that kept me banging my head against the wall is that by accessing the HTTP URL, I did not get 404 (Not Found) nor 302 (Redirect). I got 401 (Unauthorized). So I just kept trying! And boy, did I try...

When I changed the URL in the code to HTTPS, authorization worked with BOTH codes I posted.

It took a few hours... But no time is waste of time when you are learning a getting experienced.