1 subscription for multiple apps

How do I do this:
Buy one subscription (Example: “Premium Subscription” for 5$ a month) and get premium access to 20 different apps.

Each app will detect whether you have this subscription and unlock the premium content.
Each app will let you purchase this subscription, and cancel it.

How do I achieve this with android apps and google play?
Do I have to do it through a third party subscription service?

Google says this: “You can implement your own solution for sharing subscriptions across as many different apps or products as you want. For example, you could sell a subscription that gives a subscriber access to an entire collection of apps, games, or other content for a monthly or annual fee. To implement this solution, you could add your own business logic to your app to determine whether the user has already purchased a given subscription and if so, allow access to your content.”

That’s all they say about it, where do I start?

Unity natively supports InApp Purchases.

What you basically need to do is implement the same ProductID across all apps you make. There’s even a BuySubscription method as it seems.