We are talking about our Download Listings Service (DLS) here.
First of all, you are correct, the link itself won't work without the username and password in the POST request to that link. There are two options, and this will also answer your http / https question.
Option A: do one request, whcih includeds the URL as you get it from above as the target URL, but change it to HTTPS. So the URL would for example be: https://technet.rapaport.com/HTTP/RapLink/download.aspx?ShapeIDs=1&SortBy=Owner&White=1&Fancy=1&Programmatically=yes&Version=1.0
You would then pass the other parameters in your post data., which will look something like this:
formData["Username"] = "myUser";
formData["Password"] = "myPassword";
webRequest.Method = "POST";
webRequest.ContentType = "application/x-www-form-urlencoded";
Option B: do two requests, one over https to authenticate to https://technet.rapaport.com/HTTP/Authenticate.aspx retrieve the userticket from there, and connect this to the generate code URL, and then you can request over HTTP.
You can use this as a good example:
You can also try this manually, by going to this URL - https://technet.rapaport.com/HTTP/Authenticate.aspx - type in your username and password, click logon, and then copy & paste your ticket - that long string of characters - after the url + &ticket=
so for example:
Hope this helps