Speaking of shoehorning things, it doesn't look particularly "Open" to me that website owners are free to pick a limited number of authenticating authorities, instead of letting the user to pick their own.

(Imagine if e-mail adresses were considered "invalid" in forms if not from Gmail or Outlook !)

It was especially bad with last years Advent of Code, where going through OpenID (or was it OAuth ?) was the ONLY way to join, and with only 3 options listed, none of which I wanted to use !