Basic HTTP Auth with Flutter the right way

Within a Flutter app, I just tried to create a POST request to an REST API backend that requires HTTP Basic Auth using this piece of code that I have found on Stackoverflow due to lack of documentation.

String username = 'test';
  String password = '123£';
  String basicAuth =
      'Basic ' + base64Encode(utf8.encode('$username:$password'));
  print(basicAuth);

  Response r = await get('https://api.somewhere.io',
      headers: {'authorization': basicAuth});
  print(r.statusCode);
  print(r.body);

Since my abstraction required a header that was prebuilt somewhere else, I created it this way:

Map headers = {
    'content-type': 'application/json',
    'accept': 'application/json',
    'authorization': basicAuth
 };

However, somewhere within the POST request the following exception was thrown:

_InternalLinkedHashMap<dynamic, dynamic>' is not a subtype of type 'Map<String, String>' }, event: LoginButtonPressed { username: futzi, password: futz }, nextState: LoginLoading }

Turned out, the Map has do be created with real type hinting:

Map<String, String> headers = {
    'content-type': 'application/json',
    'accept': 'application/json',
    'authorization': basicAuth
 };

This works :)