This is fantastic. LDAP servers have always been atrocious.

Can anyone suggest an open source self-hosted IdP for use with SAML and/or OAuth? Specifically not looking for a cloud-hosted one, and ideally not something horrifyingly complicated like Shibboleth.

You might want to give ZITADEL a spin https://github.com/zitadel/zitadel SAML2.0 is on a PR right now, but ready to be merged very soon. Would be glad to get your feedback. (discl. I work for ZITADEL)