chore: refactor system modules

system/services/ssh.nix

@@ -0,0 +1,30 @@
+{
+  lib,
+  config,
+  ...
+}:
+with lib; let
+  cfg = config.system.services.ssh;
+in {
+  options.system.services.ssh = {
+    enable = mkEnableOption "Enables OpenSSH";
+    allowedUsers = mkOption {
+      type = types.listOf types.str;
+      example = ["alice" "bob"];
+      default = ["phundrak"];
+    };
+    passwordAuthentication = mkOption {
+      type = types.bool;
+      example = true;
+      default = false;
+    };
+  };
+  config.services.openssh = mkIf cfg.enable {
+    inherit (cfg) enable;
+    settings = {
+      AllowUsers = cfg.allowedUsers;
+      PermitRootLogin = "no";
+      PasswordAuthentication = cfg.passwordAuthentication;
+    };
+  };
+}