When you write code in Expo you are writing React Native code. Expo has two main pieces:

1. Expo CLI (expo-cli): a developer tool for creating projects, viewing logs, opening on your device, publishing, etc.

2. Expo client: an app on your phone that lets you open your projects while you're working on them, without needing to go through XCode or Android Studio, and also lets other people view them too! And if you publish it through expo-cli, people can access it at any time through the Expo client on Android or on iOS if signed in to the same account it was published with. Lastly, we also make it possible to build standalone apps so people don't have to use the Expo client to open it, and you can distribute to the app store and play store if you like.

So Expo is a set of tools built on top of React Native. These tools depend on one key belief held at Expo: it's possible to build most apps without ever needing to write native code, provided that you have a comprehensive set of APIs exposed to JavaScript.

This is important because with React Native you can always drop down to native code. This is incredibly helpful sometimes but it comes at a cost: you need to send people your binaries if you want them to test them, someone on the other side of the world can't just tap a link to open it while you're working on it and you can't just publish it with one click for someone to access it similar to how you would in a browser.

With Expo, we suggest that try to avoid dropping down to native code, if you can. As I mentioned above, we think that with a comprehensive set of APIs available to JavaScript, this shouldn't be necessary for most apps. So, we aim to provide this comprehensive set of APIs, and then build all of the awesome tooling that can exist in a world where the native runtime is shared.

However, if you must find that you want to drop down to native, you can use eject and continue using the native APIs that Expo gives you while having the same level of control as you would in any native project.

Read more about ejecting

Expo is a framework for React Native, they will both work with whatever auth solution you desire. Expo used to be very restrictive in what you could do with it (for example: it was very hard to integrate with native modules without ejecting).

But Expo has evolved greatly in the last few years, and now there are really few downsides to it.

In my opinion, go with Expo unless your requirements explicitly say otherwise.

Also, fyi, the main limitations of Expo nowadays are:

• Bigger bundle size (and thus, bigger app size)
• Slight overhead when integrating with some native libraries
• It does not work with react-native-windows and react-native-macos