It seems that in the change log from April 2019, that IDP usernames were made case-insensitive, however in 8.1.3 I’m unable to login unless the case matches for usernames.
13315: Compare usernames in a case-insensitive way
Login using an Ignition IdP now handles usernames in a case-insensitive fashion
Is this a regression?
I think that’s a slightly misleading release note…
See this thread for more context on the bug: