nixos_config/system/nix_lix.nix

{
  nix.settings.extra-substituters = [
    "https://cache.lix.systems"
  ];

  nix.settings.trusted-public-keys = [
    "cache.lix.systems:aBnZUw8zA7H35Cz2RyKFVs3H4PlGTLawyY5KRbvJR8o="
  ];
}