Presumably some HN mod changed the URL to point to something different?
HN follows redirects, and your link obviously redirects to the login page if the HN server fetches it.
Ah! Thank you! How can I update the story URL to point to GitHub's new dashboard feed?
I don't think you can, since its not a publicly accessible website.
My dashboard-feed is pretty much useless unfortunately, I have rarely used it but when I did it was useful now though there 2 out of 20 that might be useful.