Yeah, probably is. I see the same HTTP Auth login when accessing my employers intranet (Sharepoint) from Firefox.

Honestly, I’m not entirely sure.

I’ve seen the name Forgerock pop up occasionally, but I don’t know if that’s just tied to the login component on the web pages. Also, they recommend Mac users stick with Safari, which is puzzling. I mean: if it was a Microsoft product, you’d think they’d lock it down to Edge on Mac too—so that makes me wonder.

Just my thoughts—could be totally off base.

My guess -- they support Safari because of iOS. And so might as well just support it on Mac too because it's the default... Heck MS even made Teams more officially supported on Safari than Firefox!

Forgerock would make sense, though the Edge requirement is a little strange.