I have not found the function to add/create a middleware group, but these are the other ways I found to add middleware in a service provider.

public function boot( Illuminate\Routing\Router $router, \App\Http\Kernel\Kernel $kernel) {

	// Add a new middleware to beginning of the stack if it does not already exist.
	$kernel->prependMiddleware(\path\to\custom\middleware\file::class)

	// Add a new middleware to end of the stack if it does not already exist.
	$kernel->pushMiddleware(\path\to\custom\middleware\file::class)

	// Get or set the middlewares attached to the route.
	$router->middleware(\path\to\custom\middleware\file::class)

}

TerrePorter said:

I have not found the function to add/create a middleware group, but these are the other ways I found to add middleware in a service provider.

public function boot( Illuminate\Routing\Router $router, \App\Http\Kernel\Kernel $kernel) {

  // Add a new middleware to beginning of the stack if it does not already exist.
  $kernel->prependMiddleware(\path\to\custom\middleware\file::class)

  // Add a new middleware to end of the stack if it does not already exist.
  $kernel->pushMiddleware(\path\to\custom\middleware\file::class)

  // Get or set the middlewares attached to the route.
  $router->middleware(\path\to\custom\middleware\file::class)

}

Thank you for your replay. I found the solutions too, but it seems I need some workaround about it or wait till middleware group register functions will appear in router class.