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Each of these providers can then provide a credential that uniquely identifies the user in the context of this authentication provider. You can link a Firebase user to one or more authentication providers. In their Firebase Summit 2020 session “ Firebase Authentication: From fully managed to fully customizable”, my colleagues Sam and Malcolm dive into how the token exchange flow works in detail - I highly recommend watching this talk: Any authentication provider you might use in your app essentially just helps you to exchange specific credentials for a Firebase-specific ID token.
![firebase authentication ios pod firebase authentication ios pod](https://apptraitsolutions.com/wp-content/uploads/2018/12/Firebase-Authentication.jpg)
It helps to keep in mind that, at its core, a Firebase user is just a thin wrapper around an ID token. At this moment, Firebase Authentication returns an error, stating that the credential has already been linked to another Firebase user account (the one in step 7).The app tries to link the anonymous account with these credentials.The app receives Sign in with Apple credentials representing Alice.She finds the Sign in with Apple button on her iPad and signs in.As the new tasks she enters on her iPad don't show up on her iPhone, she gets suspicious and realises she needs to sign in to the app on her iPad as well.What Alice doesn't know: as she is now using a different device, she is represented by a new anonymous user ID on her iPad.Assuming that it might take a while for the data to sync from her iPhone to her iPad, she starts adding new tasks on her iPad.Upon launching the app, she sees an empty screen.
![firebase authentication ios pod firebase authentication ios pod](https://unityassetcollection.com/wp-content/uploads/2020/08/Firebase-Authentication-Android-iOS-768x512.jpg)
A while later, Alice decides to use the app on her iPad as well.Firebase Authentication upgrades the anonymous account into a permanent account, connecting it with Alice's Apple ID.The app then calls into Firebase Authentication to link Alice’s anonymous user with these credentials. The app receives a credential object from Sign in with Apple.She discovers the Sign in with Apple button and signs in using her Apple ID.She decides to sign up to take advantage of the extra features of the app, such as sharing data between multiple devices.
![firebase authentication ios pod firebase authentication ios pod](https://i.ytimg.com/vi/mPBBNi2Ou6o/maxresdefault.jpg)
FIREBASE AUTHENTICATION IOS POD SERIES
Here is an overview of the series and what we're building: This article is part of a series of articles that explores building a real-world application using SwiftUI, Firebase, and a couple of other technologies.