doco makes reference to OAuthLogin.GetAuthorizationCode...where is this class?

Hey, I also wound up in MYOB website 404 land sorting this out.  I've played with the code from KJM to spit out the auth code in a .NET core WPF app.  It's a bit rough at this stage but seems to do the trick as a replacement for the lost OAuthLogin.GetAuthorizationCode:

private string GetAuthorizationCode()
{

var redirectUri = $"http://localhost:8080/";
var developerKey = "blah blah";

var AuthorizationCodeEndpoint = "https://secure.myob.com/oauth2/account/authorize";

// Creates an HttpListener to listen for requests on that redirect URI.
var httpListener = new HttpListener();
httpListener.Prefixes.Add(redirectUri);

// Listening
httpListener.Start();

// Creates the OAuth 2.0 authorization request.
var authorizationRequest = string.Format("{0}?response_type=code&scope=CompanyFile&redirect_uri={1}&client_id={2}",
AuthorizationCodeEndpoint, System.Uri.EscapeDataString(redirectUri),
developerKey);

// Opens request in the browser.
var ps = new ProcessStartInfo(authorizationRequest)
{
UseShellExecute = true,
Verb = "open"
};
Process.Start(ps);

//System.Diagnostics.Process.Start(authorizationRequest);

// Waits for the OAuth authorization response.
var context = httpListener.GetContext();
var request = context.Request;

httpListener.Stop();

var uri = new Uri(request.Url.OriginalString);
var query = System.Web.HttpUtility.ParseQueryString(uri.Query);

var code = query.Get("code");

return code;
}