config/modules/nixos/services/vpn/default.nix

{
  lib,
  config,
  pkgs,
  ...
}:
with lib;
with lib.custom; let
  cfg = config.services.vpn;
in {
  options.services.vpn = with types; {
    enable = mkBoolOpt false "Enable VPN service(s)";
  };

  config = mkIf cfg.enable {
    services.mullvad-vpn = {
      enable = true;
      package = nixos-stable.mullvad;
    };
  };
}