Another solution is OpenLDAP (or JumpCloud) at the root and then supporting software:
OpenLDAP
├── PrivacyIDEA (TOTP/MFA with LDAP auth backend)
├──---└── SAML iDp (e.g. SimpleSAMLphp or Shibboleth) for SSO: AWS, Google, Github, Atlassian, Snowflake, Azure etc.
├── Dex (https://github.com/dexidp/dex) for anything that wants Oauth flow
├── Native LDAP for apps that support it (e.g. Metabase, Grafana)
├── Any other custom authT that supports LDAP as a backend
OpenLDAP itself isn't for the faint hearted but I've had a lot of success with JumpCloud (and Okta also have an LDAP directory service... though starting price is high).
