This was caused by a problem with the auth0 application configuration that has been resolved, this should be working again now, we can see successful logins again.
HOWEVER - DC/OS went EOL in October of 2021. There is nobody actively monitoring this Auth0 application and so further outages of this service are almost certainly guaranteed.
If you still need to use DC/OS, we strongly suggest that you patch your DC/OS clusters and disable the oauth_enabled flag and switch to using local users, to remove your dependency on this third party service.
Craig (ex-Mesosphere/D2iQ)