title: Difference between multipart form upload and NSURLSession.uploadTaskWithRequest
body: <p>Coming from the world of web programming, I'm pretty much comfortable with working with multipart form requests to upload files. However, in iOS, we have a thing called <code>NSURLSession</code> with the method <code>uploadTaskWithRequest</code>, which seems to be the method to call to do image uploads and the likes. </p>
  
  <p>Can you explain the difference between the two approach, <em>multipart form upload</em> vs <code>uploadTaskWithRequest</code>? If I already have a backend that handle multipart form uploads, what kind of adjustments that I might need so that it support <code>uploadTaskWithRequest</code> as well?</p>