{
  description = "A DNS server for the ACME DNS-01 challenge written in dependency-free nim";

  inputs.nixpkgs.url = github:NixOS/nixpkgs;

  outputs = { self, nixpkgs }:
     let
       # System types to support.
       supportedSystems = [ "x86_64-linux" "aarch64-darwin" ];

       # Helper function to generate an attrset '{ x86_64-linux = f "x86_64-linux"; ... }'.
       forAllSystems = nixpkgs.lib.genAttrs supportedSystems;

       # Nixpkgs instantiated for supported system types.
       nixpkgsFor = forAllSystems (system: import nixpkgs { inherit system; });
     in
  {
    packages = forAllSystems(system:
      let
        pkgs = nixpkgsFor.${system};
      in
      {
        default = pkgs.nimPackages.buildNimPackage {
          name = "norbert";
          src = self;
        };
      }
    );

    nixosModules.default = { config, lib, pkgs, ... }:
      with lib;
      let cfg = config.mawalu.services.norbert;
      in
    {
      options.mawalu.services.norbert = {
        enable = mkEnableOption "Enable the norbert DNS server";

        config = {
          baseDomain = mkOption {
            type = types.str;
            description = "Base domain.";
          };

          dnsPort = mkOption {
            type = types.port;
            description = "DNS server port";
            default = 15353;
          };

          apiPort = mkOption {
            type = types.port;
            description = "API port";
            default = 18000;
          };
        };

        users = mkOption {
          default = {};
          type = types.attrsOf (types.submodule {
            options = {
              password = mkOption {
                type = types.str;
                default = null;
                description = "API password for the user";
              };
            };
          });
          example = literalExpression ''
            {
              "exampleuser" = {
                password = "insecure";
              };
            }
          '';
        };
      };

      config = mkIf cfg.enable {
        systemd.services.norbert = {
          wantedBy = [ "multi-user.target" ];

          serviceConfig = let pkg = self.packages.${pkgs.system}.default;
          in {
            Restart = "on-failure";
            ExecStart = "${pkg}/bin/norbert ${pkgs.writeText "config" (generators.toINIWithGlobalSection {} {
              globalSection = cfg.config;
              sections = cfg.users;
            })}";
            DynamicUser = "yes";
            AmbientCapabilities = ["CAP_NET_BIND_SERVICE"];
          };
        };
      };
    };
  };
}