Convert one function from java to kotlin android

I have developed one app in JAVA. Now I have made one function for firebase related calls. and Working perfectly. But now I want to convert that function to kotlin also. But I was confused about how to use that function call in kotlin.

Function of Java :

public static void firebaseAuth(FirebaseAuth auth, AuthCredential authCredential, Function<Object, Void> delegate) {
    auth.signInWithCredential(authCredential).addOnCompleteListener(task -> {
        if (task.isSuccessful()) {
            delegate.apply(auth.getCurrentUser());
        } else {
            delegate.apply(task.getException());
        }
    });
}

Use of this Function in Java :

FireSignInHelper.firebaseAuth(mFireAuth, authCredential, o -> {

            if (o instanceof Exception) {
                signIn_UnSuccessful((Exception) o);
            } else if (o instanceof FirebaseUser) {
                FirePacket firePacket = new FirePacket();
                firePacket.setProvider(provider);
                firePacket.setToken(((FirebaseUser) o).getUid());
                firePacket.setFirebaseUser((FirebaseUser) o);
                signIn_Successful(firePacket);
            }
            return null;
        });

Converted Function In Kotlin :

fun firebaseAuth(auth: FirebaseAuth,
    authCredential: AuthCredential?,
    delegate: Function<Any?, Void?>
) {
    auth.signInWithCredential(authCredential!!)
        .addOnCompleteListener { task: Task<AuthResult?> ->
            if (task.isSuccessful) {
                delegate.apply(auth.currentUser)
            } else {
                delegate.apply(task.exception)
            }
        }
}

Use Converted function in kotlin:

I want to know this answer. Because I have try through Android studio but the compiler didn't convert properly. So I want to know how to use this function in kotlin.

Thanks In advance.

The way IntelliJ convert your code is correct.
However the Function interface is of no use in kotlin since functions are first-class citizens. See higher-Order Functions examples from the doc.

I think you simply want to do something like this

fun firebaseAuth(
    auth: FirebaseAuth,
    authCredential: AuthCredential?,
    listener: (Any) -> Unit
) {
    auth.signInWithCredential(authCredential!!)
        .addOnCompleteListener {
            listener.invoke(
                if (it.isSuccessful) auth.currentUser 
                else it.exception
            )                
        }
}

And then

FireSignInHelper.firebaseAuth(mFireAuth, authCredential) { 
     when(it){
        is FirebaseUser -> { ... }
        is Exception -> { ... }
     }
}