Suddenly auth request is failing

This suggests that your server can no longer reach Twitch.

This is unlikely to be a Twitch problem.
But something between your server and the Twitch Server.

This could be your servers firewall,
Your servers box provider.
Or one of the servers in the route between you and Twitch.

If it was a Twitch error you would get a HTTP code.
This is a flat “failed to connect”