AuthorizationServiceConfiguration.fromUrl support

[ChrisHux]

I am building a AppAuth service similar to #407 and i would like to have the option to use the fetchFromUrl() with the discovery url to load my service config as part of the service initialization, before atempting to log in with the service.

I saw the Android AppAuth library offers a fetchFromUrl function for the
AuthorizationServiceConfiguration so maybe there could be option to add it here as well.

final FlutterAppAuth _appAuth = FlutterAppAuth();
Completer<void> oidcInitCompleter = Completer<void>();
late final String _clientId;
late final String _discoveryUrl;
late final String _redirectUrl;
AuthorizationServiceConfiguration? _serviceConfiguration;

AppAuthService() {
    _discoveryUrl = someDiscoveryURI;
    _clientId = someClientID;
    _redirectUrl = "someURI;
    /*  Wanted Feature:
   _serviceConfiguration = await  _appAuth.fetchFromUrl(_discoveryUrl);
   */
   oidcInitCompleter.future.then((value) => notifyListeners())
}

[MaikuB]

Can you submit a PR for this?

[ChrisHux]

unfortunatly i don't have a sollution for the problem ready and don't have the capacity to implement it for the forseeable furture, i just came across it in the android appauth code.

[MaikuB]

Ok I'll leave a label to see if anyone will contribute towards it but if this remains open a while then I'll be closing it as I won't be adding this myself. One of the reasons it wasn't originally done was this is something devs could implement this themselves within their app. What happens behinds the scenes is that the discovery document is download and parsed. Developers can do this entirely with Dart/Flutter without this plugin. Furthermore, they can do it with their chosen HTTP client and library for decoding JSON