How do I execute HTTPRequest with Binary Data?

I’m playing with Salesforce in Mathematica trying to automate some PDF upload. I would like to know how can I execute the HTTPRequest as described by the curl below:

Here is the link for Salesforce website with copyable text.

How I do insert data where the text says: “Binary data goes here”? What is this HTTPRequest structure?

Any clue?

Crosspost in SE link.

Check out https://stackoverflow.com/questions/5853134/upload-to-ifile-it-through-mathematica.