How to use Steam (OpenId) to login into my Firebase powered Flutter app?

I'm building a Flutter app and I want users to be able to login through Steam (OpenId). The app is powered by Firebase.

I'm pretty new to the whole OpenId world and I've read into it but I'm still not getting it.

I found that Firebase Supports signinWithCustomToken so I think I should get the Steam OpenId to get me one of those. I also found two packages which might help me but I couldn't get those to work either:

1. https://pub.dev/packages/openid_client
2. https://pub.dev/packages/steam_login

If tried the following sample from the openid_client package:

_authenticate(Uri uri, String clientId, List<String> scopes) async {
    try {
      var issuer = await Issuer.discover(uri);
      var client = Client(issuer, clientId);

      print('CLAIMS:');
      print(issuer.claimsMap);

      urlLauncher(String url) async {
        if (await canLaunch(url)) {
          await launch(url, forceWebView: true);
        } else {
          throw 'Could not launch $url';
        }
      }

      var authenticator = Authenticator(client,
          scopes: scopes, port: 4000, urlLancher: urlLauncher);

      var c = await authenticator.authorize();

      closeWebView();

      print(await c.getUserInfo());
    }catch (err) {
      print(err);
    }
  }

But I have no idea what to give as the uri, clientId and scopes. For the uri I've tried https://steamcommunity.com/openid but when I try this I'm getting an error that it tried to Json.parse a xml response.

I've also tried the example for the steam_login package here, but that does nothing and doesn't feel like it should work within a Flutter app (even though the package states it Flutter compatible).

So if anybody could explain to me how I could achieve this with a working sample that would be great. If I get this to work I'm planning on creating a tutorial/guide for it for others.