the back button does not work in firebase ui Android

I am using firebase ui to login and register the users, my application starts with firebase ui, when I press the back button, UI the firebase Authentication UI it restarts again, every time I press the back button. how can I end the activity by pressing the back button

this is part of my code

 @Override
protected void onStart() {
    super.onStart();
    auth.addAuthStateListener(listener);

}

@Override
protected void onStop() {
    if (listener != null)
     auth.removeAuthStateListener(listener);
    disposable.clear();
    super.onStop();
}
 private void Init() {
    //Init Firebase
    auth = FirebaseAuth.getInstance();
    db = FirebaseDatabase.getInstance();
    users = db.getReference(Common.user_rider_tbl);



    providers = Arrays.asList(new AuthUI.IdpConfig.PhoneBuilder().build(),
            new AuthUI.IdpConfig.EmailBuilder().build(),
            new AuthUI.IdpConfig.GoogleBuilder().build(),
            new AuthUI.IdpConfig.FacebookBuilder().build());



    listener = new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            FirebaseUser user = firebaseAuth.getCurrentUser();

            if (user != null) {
                //Account is already logged in
                CheckUserFromFirebase(user);
            } else {
                SignWithPhone();
            }
        }
    };
}

private void SignWithPhone() {

    startActivityForResult(
            AuthUI.getInstance()
                    .createSignInIntentBuilder()
                    .setTheme(R.style.LoginTheme)
                    .setIsSmartLockEnabled(false)
                    .setLogo(R.drawable.logo)

                    .setAvailableProviders(providers)
                    .build(),
            APP_REQUEST_CODE);
}

   @Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);


    if (requestCode == APP_REQUEST_CODE) {
        IdpResponse response = IdpResponse.fromResultIntent(data);
       providerType = response.getProviderType();

        if (resultCode == RESULT_OK) {

            FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();


        } else {
            if (response == null) {
                // User pressed back button. NOTE: This is where the back action is
                //taken care of

              finish();

            }

            if (Objects.requireNonNull(response.getError()).getErrorCode() == ErrorCodes.NO_NETWORK) {
                //Show No Internet Notification
                return;
            }
            if (response.getError().getErrorCode() == ErrorCodes.UNKNOWN_ERROR)
            {
                Log.i(TAG, "EEERRROORRRR: "+ response.getError().getErrorCode());
               return;
            }


            Log.i(TAG, "EEERRROORRRR: "+ response.getError().getErrorCode());


        }
    }
}

can you help me, please