add a yubikey module

modules/yubikey.nix

@@ -0,0 +1,24 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  cfg = config.services.rad-dev.yubikey;
+in
+{
+  options = {
+    services.rad-dev.yubikey = {
+      enable = lib.mkEnableOption "enable yubikey defaults";
+      enable-desktop-app = lib.mkEnableOption "installs desktop application";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    # enable the smart card daemon for certain yubikey operations
+    services.pcscd.enable = true;
+
+    environment.systemPackages = lib.optionals cfg.enable-desktop-app [ pkgs.yubioath-flutter ];
+  };
+}