main gripes about oauth / openid are you phone home to the provider on every login, and the protocol is sufficiently nonstandard to be bad for self hosters

like if you want to use oauth to access your own google calendar, you have to go to the developer console, draw a pentagram of week-old chicken's blood that has turned dark, create an entire new cloud project, incant backwards latin, etc

per:

1. https://docs.simplecalendar.io/google-api-key/

2. 7 steps and 6 scopes to use dav https://developers.google.com/calendar/caldav/v2/auth

3. https://support.google.com/googleapi/answer/6158862?hl=en