Flutter Firebase: I want to stream the details of the logged in user across the app using Stream provider

I'm getting the below error:

The return type 'AuthUser?' isn't a 'User?', as required by the closure's context.

From the below code:

class AuthService {
  final FirebaseAuth authInstance = FirebaseAuth.instance;
  final FirebaseFirestore firestoreInstance = FirebaseFirestore.instance;

  Stream<User?> get currentUser => authInstance.authStateChanges().map(
        (User? firebaseUser) => (firebaseUser != null) ? AuthUser.fromFirebaseUser(user: firebaseUser) : null,
      );
}

Below is the code for the model class:

import 'package:firebase_auth/firebase_auth.dart';

class AuthUser {
  String? uid;
  String? email;
  String? userName;

  AuthUser({
    required this.uid,
    required this.email,
    required this.userName,
  });

  AuthUser.fromFirebaseUser({User? user}) {
    uid = user!.uid;
    email = user.email;
    userName = user.displayName;
  }
}

I would also like to know how to consume this stream using the StreamProvider<AuthUser>.value.

Are either of Consumer widget or the Provider.of(context) widget appropriate to access the values?

Your stream is mapping the User model from Firebase to your AuthUser model. So you need to change the return type of the currentUser getter.

Change this:

Stream<User?> get currentUser => authInstance.authStateChanges().map(
        (User? firebaseUser) => (firebaseUser != null) ? AuthUser.fromFirebaseUser(user: firebaseUser) : null,
);

to this:

Stream<AuthUser?> get currentUser => authInstance.authStateChanges().map(
        (User? firebaseUser) => (firebaseUser != null) ? AuthUser.fromFirebaseUser(user: firebaseUser) : null,
);