Out the box json support in .NET is a bit lacking, so people usually turn to 3rd parties (including Microsoft) to manipulate JSON. The most popular I would say is JSON.NET, and is what I use normally.
You'll find in Nuget, or can download directly.
Once you've done that, from memory you could do something like:
JObject item = JObject.Parse(<your string="">);
string login = (string)item["Login ID];
That may not be exactly right, but it gives you the gist.
Sorry, I have no clue how its done in JavaScript, but bearing in mind that's where JSON comes from, I'd expect it to be extremely simple.