All this is probably too new for it to be any good tutorials or examples available, at least I could not find any and I spent quite some time looking. I also spent quite a few hours getting it to work, but here it is:

Solution

I used the plugin cordova-plugin-apple-login (version 1.0.0) so go ahead and install it using:

npm i cordova-plugin-apple-login
ionic cordova plugin add cordova-plugin-apple-login

Note that there is no Ionic Native wrapper for the plugin, so you have to declare it instead of importing it on your page:

declare var SignInWithApple: any;

This is the login function:

 loginWithApple() {

    SignInWithApple.request({requestedScopes: [ SignInWithApple.Scope.Email, SignInWithApple.Scope.FullName ]})
    .then((appleCredential) => {
      const credential =  new firebase.auth.OAuthProvider('apple.com').credential(appleCredential.identityToken);
      this.afAuth.auth.signInWithCredential(credential)
      .then((response) => {
        console.log('Login successful');
      })
      .catch((error) => {
        console.log(error);
        alert('error:' + JSON.stringify(error));
      });
    });

  }

This was done using Ionic 4 / Angular, AngularFire2 5.30 and the cordova-plugin-apple-login 1.0.0

Configuration

You also have to do some configurations…

-> Xcode: Add capability for Sign in with Apple
-> Apple Developer: Add Services id
-> Firebase console: Add Sign-in method for Apple, leave all fields blank if you only use on iOS

If you want to support Android and or Web / PWA, you will need to do some more configuring.

Did this solution help you?

Please comment if it did, or if you had a problem with it. Also if you got it working (or not) using other versions of plugins, frameworks etc or if you found a better solution – it will help others!

P.s. I also posted this solution to Stack Overflow (my first anwer there, yay!)