I'm porting code for custom DataType from U8 to U9.
This DataType is calling a Surface controller to retrieve some data.

In the Umbraco v version I access the URL from the "Umbraco.Sys.ServerVariables" like:

var apiUrl = Umbraco.Sys.ServerVariables['MainKey']['Controller1URL'];

We set the value to this variable on project startup on the event ServerVariablesParser.Parsing like:

    // https://our.umbraco.com/documentation/extending/version7-assets
    public class BackofficeControllersURLListRegistrator : IComponent
    {
        public void Initialize()
        {
            Umbraco.Web.JavaScript.ServerVariablesParser.Parsing += ServerVariablesParser_Parsing;
        }

        private void ServerVariablesParser_Parsing(object sender, Dictionary<string, object> e)
        {
            if (HttpContext.Current == null) throw new InvalidOperationException("HttpContext is null.");

            var backofficseUrls = new Dictionary<string, string>();

            var url = new System.Web.Mvc.UrlHelper(new RequestContext(new HttpContextWrapper(HttpContext.Current), new RouteData()));
            backofficseUrls.Add(
                "Controller1URL", url.GetUmbracoApiService<Controllers.ApiControllers.Test1Controller>(controller => controller.TestFunction())
            );

            e.Add("MainKey", backofficseUrls);
        }

        public void Terminate()
        {
        }
    }

How would we in Umbraco 9 hook up to ServerVariablesParser Notification if it exists and how to retrieve Controller function URL, so I can retreave it in DataType JS code like in previus versions?

Any help would be extremally appreciated.