Until fairly recently I was able to log in with my copy of Snap! (either localhost or on github.io). Now when I login it says I've successfully logged in but I'm not logged in. No errors in the console. You can try it at https://ecraft2learn.github.io/ai/snap/snap-no-logging.html
I realize that the server needs to careful that it isn't being misused but why the change?
That never worked for me! I run a localhost copy, and I get cloud error messages if I try to save projects or load non-public ones. We're pretty flexible about special-casing known extensions, though, if you give us the specific URL (I mean, not just "github.io").
... and also, we don't want to get inundated with bug reports because some project on s.b.e doesn't work in someone's mod, or because a project made in someone's mod uses features not in actual Snap!.