nixos-combined-flake/modules/nixos/base/binary-cache/default.nix

{
  
  nix = {
    settings = {
      substituters = [
        "https://nix-community.cachix.org"
      ];
      trusted-public-keys = [
        "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
      ];
    };
  };
  }