title: C# and MIME multipart messages creation
body: <p>I need to send to Web Service a POST request with body that is represented as "multipart/form-data" Content-type.</p>
  
  <p>The sample of the body is the following:</p>
  
  <pre><code>Content-Type:multipart/form-data; boundary=WebBoundary
  
  --WebBoundary
  Content-Disposition: form-data; name="Key#1"
  Value#1
  
  --WebBoundary
  Content-Disposition: form-data; name="Key#2"
  Value#2
  
  --WebBoundary
  Content-Disposition: form-data; name="FileKey"; filename="file.jpg"
  Content-Type: image/png
  
  --WebBoundary--
  </code></pre>
  
  <p>How can I construct MIME message for this use case using HttpWebRequest?
  I want also to customize data I send. For example at first I send 3 keys where 2 keys are strings and one is image, and other time I want to send 5 keys of image type.
  Anyway I didn't find in .NET library how to do it.</p>
  
  <p>If anyone has a solution for this, I'll appreciate it.</p>
  
  <p>Thank you in advance.</p>