nixos-config/modules/system/services/server/webserver/nginx/user/default.nix

{ config, lib, ... }:
{
  users = lib.mkIf config.services.nginx.enable {
    users.nginx = {
      group = "nginx";
      extraGroups = [
        "turnserver"
        "virtualMail"
      ];
      isSystemUser = true;
      uid = 60;
    };
    groups.nginx = {};
  };
}