OpenSSH 10.0 tightened AuthorizedKeysCommand security by checking every
path component of the command binary for group/world-write permission.
/nix/store is 1775 (group-writable by nixbld), so sshd silently skips
the command for any binary in the Nix store — causing IPA pubkey auth to
silently fail with no diagnostic.
Fix: copy sss_ssh_authorizedkeys to /usr/local/bin via systemd tmpfiles
(C+ copies the file rather than symlinking, so the path at runtime is
root-owned/755 throughout), and point AuthorizedKeysCommand at the copy.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>