C#

public void loginToSite()
        {
            string formUrl = "http://www.govconnection.com/IPA/Account/Login.htm"; // NOTE: This is the URL the form POSTs to, not the URL of the form (you can find this in the "action" attribute of the HTML's form tag
            string formParams = "__EVENTTARGET=&__EVENTARGUMENT=&__VIEWSTATE=%2FwEPDwUJNjYxOTQ0NzIyD2QWAmYPZBYCAgYQFgIeCG9uc3VibWl0BRxyZXR1cm4gQ29tcGxldGVBc3luY0NhbGxzKCk7ZBYCAgcPDxYEHghDc3NDbGFzcwUNc2l0ZUNvbnRhaW5lch4EXyFTQgICZBYEAgEPDxYEHwEFI2ZhdXhDb2x1bW5XcmFwIGNsZWFyIHdpdGhCYWNrZ3JvdW5kHwICAmQWAgIBDw8WBB8BBQdjb250ZW50HwICAmQWBgIBD2QWBgIBDxYCHgdWaXNpYmxlaBYEAgEPFgIfA2hkAgMPDxYCHwNoZGQCAw9kFgICAg8QZGQUKwACMtMBAAEAAAD%2F%2F%2F%2F%2FAQAAAAAAAAAMAgAAAEBJUEEuV2ViLCBWZXJzaW9uPTUuMC42MTEuMSwgQ3VsdHVyZT1uZXV0cmFsLCBQdWJsaWNLZXlUb2tlbj1udWxsBQEAAAAuSVBBLldlYi5VSS5Db250cm9scy5Ecm9wRG93bkxpc3RzLkRyb3Bkb3duSXRlbQQAAAAGX3ZhbHVlBV90ZXh0CV9zZWxlY3RlZBRfSXNUcmFja2luZ1ZpZXdTdGF0ZQEBAAABAQIAAAAGAwAAAAAJAwAAAAAACwL%2F%2F%2F%2F%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%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&ctl00%24Content%24ctl04=0&ctl00%24Content%24ctl00%24emailAddressTextBox=EMAILGOESHERE&ctl00%24Content%24ctl00%24passwordTextBox=PASSWORDGOESHERE&ctl00%24Content%24ctl00%24loginImageButton.x=0&ctl00%24Content%24ctl00%24loginImageButton.y=0&ctl00%24_leftColumn%24ctl00=&ctl00%24_header%24txtProductSearch=Item%23%2C+MFG%23+or+Keyword";
            string cookieHeader;
            System.Net.HttpWebRequest req = (HttpWebRequest)System.Net.WebRequest.Create(formUrl);
            req.AllowAutoRedirect = true;
            req.ContentType = "application/x-www-form-urlencoded";
            req.Method = "POST";
            byte[] bytes = Encoding.ASCII.GetBytes(formParams);
            req.ContentLength = bytes.Length;
            using (Stream os = req.GetRequestStream())
            {
                os.Write(bytes, 0, bytes.Length);
            }
            WebResponse resp = req.GetResponse();

            StreamReader sr = new StreamReader(resp.GetResponseStream());
            String result = sr.ReadToEnd();
            MessageBox.Show(result);
            cookieHeader = resp.Headers["Set-cookie"];
        }

RasSetEntryDialParams