Add option for networkmanager configuration.

config/networkmanager.nix

@@ -0,0 +1,26 @@
+{
+  pkgs,
+  config,
+  lib,
+  ...
+}:
+
+with lib;
+mkIf (elem "networkmanager" config.machine.conffiles) {
+
+  networking = {
+    inherit (config.machine) hostName;
+  };
+
+  networking.networkmanager = {
+    enable = true;
+    plugins = with pkgs; [
+      networkmanager-openconnect
+    ];
+  };
+
+  environment.systemPackages = with pkgs; [
+    networkmanagerapplet
+    networkmanager_dmenu
+  ];
+}