webview_flutter как добавить параметр header при изменении url

String URL = 'https://...../login-app?authkey=${globals.authkey}&test=1';
  WebViewController _webViewController;
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: new AppBar(),
body: WebView(
        // initialUrl: 'https://...../login-app?authkey=${globals.authkey}',
        javascriptMode: JavascriptMode.unrestricted,
        onWebViewCreated: (WebViewController webViewController) {
          _controller.complete(webViewController);
          webViewController.loadUrl(URL,headers: {"SB-app": "iphone"},);
        },
        navigationDelegate: (NavigationRequest request) async {
          print('allowing navigation to $request');
          if(request.url.contains('driver/chat') || request.url.contains('driver/on-map') || request.url.contains('driver/passanger-form') || request.url.contains('driver/login')) {
            _webViewController.loadUrl(request.url, headers: {"SB-app": "iphone"});
          }
          return NavigationDecision.navigate;
        },
        onPageStarted: (String url) async {
          print('Page started loading: $url');
        },
        onPageFinished: (String url) async {
          print('Page finished loading: $url');
        },