Hi everyone, just a few notes to share - hopefully it may save time for someone else:

My Custom Action based on the code from Stephen Chew and Daniel Joshi as a base, with some modifications
However, had an issue that user can be created only once. Next attempts to create user do not work with the message \"[firebase_auth/network-request-failed] A network AuthError (such as timeout, interrupted connection or unreachable host) has occurred. \" in the logs
Apparently this error is caused by something inside Firebase SDK, when you're using the same FirebaseApp app name and it's not a network error. Hours of debugging didn't help me to find the reason for this: FirebaseApp app instance is destroyed properly in the end, time limits are respected, tried with user signoff, etc.

So the working solution was to use this approach:

  String uniqueAppName = 'Secondary_${DateTime.now().millisecondsSinceEpoch}';\n  FirebaseApp app = await Firebase.initializeApp(\n      name: uniqueAppName, options: Firebase.app().options);

With this multiple users could be created. However, it might be useful to disable the persisting storage for these \"secondary\" instances, so that user credentials aren't stored in browser storage (indexedDB):
```
  await firebase_auth.FirebaseAuth.instanceFor(app: app)\n      .setPersistence(Persistence.NONE);
```
If anyone could shed some light why user creation doesn't work with the same FirebaseApp app name - I'd be very curious to know it.

Creating Users from an Admin Account