After spending months writing an app, I expected the final step — putting it on the App Store — to feel like a programming task. It mostly did not. The application can work perfectly on my phone and still be nowhere near ready for submission.
One of the nicest things about Expo is how easy it makes the beginning of a React Native project. You write some code, scan a QR code and suddenly the app is running on your phone. For a while, that creates the impression that mobile development is basically web development with a different UI.
Adding Google Sign-In sounded like one of those features that should be simple: add a button, open Google, get the user back into the app and save their account. In practice, the interesting part was not the button at all. It was understanding that authentication involves several systems agreeing on the identity of the same application.