Firebase.kt

//1) inject a datasource and repository, which is passed to the constructor of the ViewModel
@Singleton
class LoginDataSource  @Inject constructor(){
    private var mAuth: FirebaseAuth. ...//
    
class LoginRepository @Inject constructor(val dataSource: LoginDataSource) { ...

//2) use the Executor overload from the DataSource:
   var executor: ThreadPoolExecutor = ThreadPoolExecutor(
        numCores * 2, numCores * 2,
        60L, TimeUnit.SECONDS, LinkedBlockingQueue<Runnable>()
    )
    fun login(email: String, password: String, liveData: MutableLiveData<Result>) {
         mAuth.signInWithEmailAndPassword(email, password)
            .addOnCompleteListener(
                executor,
                OnCompleteListener<AuthResult?> { task ->
                    if (task.isSuccessful) {
                        // Sign in success, update UI with the signed-in user's information
                        Log.d(TAG, "signInWithEmail:success")
                        val user = mAuth.currentUser
                        val result = Result()
                        result.data = user as FirebaseUser
                        result.status = Status.SUCCESS
                        liveData.postValue(result)
//3) The LiveData is passed in from the VM:
 fun login(email: String, password: String, liveData: MutableLiveData<Result>) {
 
// and observed in the fragment