feat: automate SSH config ('known_hosts', 'authorized_keys' ...)

modules/ssh/known-hosts.nix

@@ -0,0 +1,19 @@
+{
+  lib,
+  config,
+  outputs,
+  ...
+}:
+let
+  hosts = lib.attrNames outputs.nixosConfigurations;
+  hostsWithKeys = lib.filter (
+    hostname: builtins.pathExists ../../hosts/${hostname}/ssh_host.pub
+  ) hosts;
+in
+{
+  # auto generate known_hosts for all hosts in flake
+  programs.ssh.knownHosts = lib.genAttrs hostsWithKeys (hostname: {
+    publicKeyFile = ../../hosts/${hostname}/ssh_host.pub;
+    extraHostNames = lib.optional (hostname == config.networking.hostName) "localhost";
+  });
+}