{ lib, ... }:
  let
    inherit (lib)
      mkOption
      types
    ;

    userType = types.submodule (
      { ... }: {
        options = {
          displayName = mkOption {
            type = types.nullOr types.str;
            description = "The human-readable name of the user.";
            default = null;
          };

          mailAddress = mkOption {
            type = types.nullOr types.str;
            description = "The mail address of the user.";
            default = null;
          };

          groups = mkOption {
            type = types.listOf types.str;
            description = "The additional groups of the user.";
            default = [];
          };

          defaultShell = mkOption {
            type = types.nullOr types.str;
            description = "The default shell of the user.";
            default = null;
          };

          git = (import ./git/options.nix) { inherit lib; };
        };
      });
  in {
    options = {
      valhalla = {
        users = mkOption {
          type = types.attrsOf userType;
          description = "The users to create on the machine.";
          default = {};
        };
      };
    };
  }