assignment2.dart

import 'package:http/http.dart' as http;

Future<String> getIdToken({bool? force}) async {
  // fetch update token
  return "abc*******";
}

Future<void> main() async {
  final client = http.Client();
  final token = await getIdToken();

  final response = getRequest(client, token);

  if (response.statusCode == 401) {
    getRequest(client, token);
  } else {
    ///other process
  }
}

getRequest(client, token) async {
  await client.get(Uri.parse("https://senkyaku.jp"),
      headers: {"Authorisation": "Bearer $token"});
}