Unfortunately, the notification file is accessible only when you’re already logged in. I tried accessing it with curl -u, using my username and password, but it does not support HTTP authentication. Your second link mentions API keys, but I don’t see how to generate it on the forum. I’m not even sure the forum provides an API …
It sounds like the ability to get an API key is turned on by default, but there are some hoops you need to go through to generate. Maybe there should be a feature request to create a discourse integration.