public static IServiceCollection AddMaintenance(this IServiceCollection services, MaintenanceWindow window)
 {
     services.AddSingleton(window);
     return(services);
 }
 public MaintenanceMiddleware(RequestDelegate next, MaintenanceWindow window, ILogger <MaintenanceMiddleware> logger)
 {
     this.next   = next;
     this.logger = logger;
     this.window = window;
 }