I am trying to figure out how I can retain personal SSH keys (probably the most important part, or at least important to have an alternative connection method) while also having modern tools like SSO or at least SAML, some way to federate to different ADs.

I know there are a few things out there like Authentik and Authelia, but not 100% sure Authentik covers those needs above. Does anyone have experience with these or other modern LDAP alternatives that work well with Linux?