Rapaport TechNet
 
Full HTTP POST/WebRequest Example (C#) and CSV file

using System;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.IO;
using System.Collections.Specialized;

namespace TechnetSamples
{
class Program
{
static void Main(string[] args)
{
string URLAuth = "https://technet.rapaport.com/HTTP/Authenticate.aspx";
WebClient webClient = new WebClient();

NameValueCollection formData = new NameValueCollection();
formData["Username"] = "myUser";
formData["Password"] = "myPassword";

byte[] responseBytes = webClient.UploadValues(URLAuth, "POST", formData);
string resultAuthTicket = Encoding.UTF8.GetString(responseBytes);
webClient.Dispose();

string URL = "http://technet.rapaport.com/HTTP/Upload/Upload.aspx?Method=file";
string boundary = "----------------------------" + DateTime.Now.Ticks.ToString("x");
System.Net.WebRequest webRequest = System.Net.WebRequest.Create(URL);

webRequest.Method = "POST";
webRequest.ContentType = "multipart/form-data; boundary=" + boundary;

string FilePath = "C:\\test.csv";
formData.Clear();
formData["ticket"] = resultAuthTicket;
formData["ReplaceAll"] = "false";

Stream postDataStream = GetPostStream(FilePath, formData, boundary);

webRequest.ContentLength = postDataStream.Length;
Stream reqStream = webRequest.GetRequestStream();

postDataStream.Position = 0;

byte[] buffer = new byte[1024];
int bytesRead = 0;

while ((bytesRead = postDataStream.Read(buffer, 0, buffer.Length)) != 0)
{
reqStream.Write(buffer, 0, bytesRead);
}

postDataStream.Close();
reqStream.Close();

StreamReader sr = new StreamReader(webRequest.GetResponse().GetResponseStream());
string Result = sr.ReadToEnd();
}

private static Stream GetPostStream(string filePath, NameValueCollection formData, string boundary)
{
Stream postDataStream = new System.IO.MemoryStream();

//adding form data
string formDataHeaderTemplate = Environment.NewLine + "--" + boundary + Environment.NewLine +
"Content-Disposition: form-data; name=\"{0}\";" + Environment.NewLine + Environment .NewLine + "{1}";

foreach (string key in formData.Keys)
{
byte[] formItemBytes = System.Text.Encoding.UTF8.GetBytes(string.Format(formDataHeaderTemplate,
key, formData[key]));
postDataStream.Write(formItemBytes, 0, formItemBytes.Length);
}

//adding file data
FileInfo fileInfo = new FileInfo(filePath);

string fileHeaderTemplate = Environment.NewLine + "--" + boundary + Environment.NewLine +
"Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"" +
Environment.NewLine + "Content-Type: application/vnd.ms-excel" + Environment.NewLine + Environment.NewLine;

byte[] fileHeaderBytes = System.Text.Encoding.UTF8.GetBytes(string.Format(fileHeaderTemplate,
"UploadCSVFile", fileInfo.FullName));

postDataStream.Write(fileHeaderBytes, 0, fileHeaderBytes.Length);

FileStream fileStream = fileInfo.OpenRead();

byte[] buffer = new byte[1024];

int bytesRead = 0;

while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
{
postDataStream.Write(buffer, 0, bytesRead);
}

fileStream.Close();

byte[] endBoundaryBytes = System.Text.Encoding.UTF8.GetBytes("--" + boundary + "--");
postDataStream.Write(endBoundaryBytes, 0, endBoundaryBytes.Length);

return postDataStream;
}
}
}