android-auth | Spotify authentication and authorization for Android | OAuth library

I'm making an authenticator following the tutorial: http://blog.udinic.com/2013/04/24/write-your-own-android-authenticator/

The login Activity requires to extend AccountAuthenticatorActivity, the issue starts here: AccountAuthenticatorActivity extends the regular Activity and not AppCompatActivity.

Using the regular Activity in AppCompat results in a Activity without ActionBar. I want to use AccountAuthenticatorActivity AND having an ActionBar.

I am trying to take WhatsApp's approach to contact lists, where I simply sync my app's contacts with the devices contacts. I am using Firebase as my Authentication Platform and Database (Firestore). I am using Firebase Auth UI for Phone Number Authentication.

What I would like to achieve is my In-App contacts list basically load with my device contacts ONLY if those contacts have my app installed as well. Just like WhatsApp does.

I have already read the official docs for AccountManager and seen a few tutorials like this one but cannot figure out how to put it all together.

Questions I have are:

1. What exactly is the role of the AccountAuthenticator and for what purpose would a developer use it? Do I need an AccountAuthenticator for my use case? Do I just need to do AccountManager.addAccountExplicitly() and that's it?

2. If I do need the whole API, how do I set it up with my Firebase Auth UI? The Auth UI is already handling the login flow and everything and I'm already storing a user object in Firestore.

3. In AccountManager.addAccountExplicitly(accountName, accountType), what is Account Name supposed to be and Account Type supposed to be? Give an example.

Here Is My Current Code For Firebase Authentication:

I have tried to start the 3DES protocol on a Mifare Ultralight C. In the product datasheet they specify that you have to start by sending the command 1A (and I found this post that everyone who asks is redirected to: Android: Authenticating with NXP MiFare Ultralight C).

So I tried to do something similar in the code below:

I'm trying to create an AccountAuthenticator to be used with multiple of our apps (so one account in the system-settings used by multiple apps). Just like all Google-apps use the same account on the system.

The problem is: How can I set it up that only one app (we don't know which it will be) needs to be installed and when a second app gets installed, it can just re-use an existing account?

I've created my AccountAuthenticator using this tutorial and embedded into a library-project which gets included in all our apps. This works fine when only one app is installed.

As soon as a second app gets installed and the user tries to login, the system shows the intent-chooser dialog where he can pick both of our apps (because they both use the same authenticator-library with the same intent-filter). This should be the problem as well here (but I havn't verified it yet).

With some research you'll stumble across sharedUserId and this tutorial. But this "solution" has the problem, that you need some kind of always-first-installed app with the authenticator in it. Plus, with the new Google Play App Signing a sharedUserId seems impossible because every app will be signed with a different signature.

There might be a way to grant other apps access to the authenticator but there's still the problem that the authenticator-app needs to be installed first (as suggested here).

How can I solve this? How can I share an AccountAuthenticator with multiple apps without installing an app holding it first? How does Google do it? Do they have their authenticator in the Play Services?

I am following the Spotify SDK tutorial, and trying to make a RN module for my application. This is my SpotifyModule.m code: