lib:
nixosConfigurations:

let
  sshKnownHostsTxt = builtins.toFile "known_hosts" (lib.concatMapStrings
    (hostName:
      let d = nixosConfigurations.${hostName}.config.deploy;
      in lib.concatMapStrings (key: "${d.ssh.HostName} ${key}\n") d.sshPublicKeys
    )
    (builtins.attrNames nixosConfigurations)
  );

  attrsToList = lib.mapAttrsToList (n: v: "${n} ${v}");
  attrsToLines = a: lib.concatLines (attrsToList a);

in
lib.concatMapStrings
  (host: ''
    Host ${host}
    UserKnownHostsFile ${sshKnownHostsTxt}
    ${attrsToLines nixosConfigurations.${host}.config.deploy.ssh}
  '')
  (builtins.attrNames nixosConfigurations)