I am trying to post to a 4chan-like imageboard using .NET. Since the imageboard software offers no API, I want to build the POST manually using HttpClient.

To begin, I opened the Network tab through the dev console in Chrome. I then made my post through the web page like I normally would by entering the text in the textbox and clicking the submit button. The idea is that I can look at the request as sent through Chrome and then write .NET code to build new requests with parameters I pass in. However, it turns out to be more complicated than I thought.

Can anyone provide some starter code that builds the below request using System.Net.Http.HttpClient? I am not expecting anyone to do the entire request message, just the distinctly differently components. I could build the rest.

Here's the request message output as copied directly out of Chrome:

https://pastebin.com/14qVn2Pg

Had to use pastebin because Reddit's text formatting sucks.