Can't really speak to the point of the guy you're replying to, but the FreeIPA implementation via SSSD does more than just Kerberos tickets. Actually, I think the Kerberos based stuff as it relates to SSH is GSSAPI as part of sshd itself and has little to do with sssd, though I could be wrong.

That said...

If I'm remembering things correctly (and it's been a looong while since I've played with this), FreeIPA's client configures sshd with an AuthorizedKeysCommand that executes a program that queries sssd for the list of authorized keys for a given user. Sssd then uses a plugin to query the LDAP server @ FreeIPA to get the list of keys.

There's also SSHFP (I think) records in DNS if you're using FreeIPA's DNS servers. These provide the host keys for servers for your ssh client to check against. Not sure if that's integrated into ssh itself or something else -- I can't remember how it's implemented offhand -- but it's fairly nifty since you never see the TOFU prompt (or it would be if DNS was actually secure, anyway).