How to fix `Do not use BuildContexts across async gaps` in a StatelessWidget?

Question

During a FireAuth process, I need to store a user instance in my ChangeNotifier appState.

Therefore I am meant to do that:

Provider.of<StateModel>(context, listen: false).signedIn = shokazeUser;

Unfortunately, I must fetch the shokazeUser from the remote database via an await modifier. But doing so, I am exposed to the fact the context might no longer be valid. I got the error:

Do not use BuildContexts across async gaps.

Because I am in a StatelessWidget I can't do what would do in a StatefulWidget aka testing mounted.

What to do then?

My code's as follows:

 Future<String?> _authUser(BuildContext context, LoginData data) {
    debugPrint('Name: ${data.name}, Password: ${data.password}');

    return auth
        .signInWithEmailAndPassword(email: data.name, password: data.password)
        .then((credential) async {
      try {
        final user = credential.user;

        if (user == null) {
          return 'Password does not match';
        } else {
          // == Tell the app we just signed in

          try {
            final shokazeUser = await shokaze.User.getFromId(user.uid);
            if (shokazeUser == null) {
              return "Unable to fetch user from database";
            }
            Provider.of<StateModel>(context, listen: false).signedIn =
                shokazeUser;
          } catch (e) {
            return "Error while fetching user from database: $e";
          }
          return null;
        }
      } catch (e) {
        return 'User not exists';
      }
    }).catchError((e) {
      if (e.code == 'weak-password') {
        debugPrint('The password provided is too weak.');
      } else if (e.code == 'email-already-in-use') {
        debugPrint('The account already exists for that email.');
      } else {
        debugPrint(e.toString());
      }

      return Future<String?>.error(e);
    });