Fixing onAuthStateChanged and getRedirectResult Returning Null User After Google Login Redirect

Encountering issues with Firebase authentication on iOS where users see null after Google login? Discover the cause and solution in our detailed guide!
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This video is based on the question https://stackoverflow.com/q/74846216/ asked by the user 'Dave' ( https://stackoverflow.com/u/326174/ ) and on the answer https://stackoverflow.com/a/75794833/ provided by the user 'Dave' ( https://stackoverflow.com/u/326174/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Firebase Authentication Issue: onAuthStateChanged and getRedirectResult Returning Null User

If you're a developer working with Firebase authentication and React, you might have encountered a frustrating issue: after a successful Google login, some users see a null user state in your application. This problem seems to be especially prevalent among iOS users, with reports indicating it affects roughly 1 out of 10 users. In this guide, we'll delve into the problem and provide a comprehensive solution to ensure your users can log in without a hitch.

The Problem: Null User State After Successful Login

The core of the problem arises when users attempt to authenticate with Google and are redirected back to the application. After this redirect, the following happens:

The onAuthStateChanged event fires

However, the user object is null, despite the fact that the login was successful.

This issue can be particularly tricky because it happens inconsistently, often linked to users who might be trying to utilize multiple authentication providers at once. Without clear error messages or logs, it appears as though the application is reinitializing, leaving developers puzzled.

Understanding the Complexity

As described in the original query, the authentication process flows like this:

A user selects their Google account and is redirected back to the application.

The application attempts to manage the authentication state changes using the Firebase auth library, specifically onAuthStateChanged, and it tries to handle the result with getRedirectResult.

When these functions do not yield the expected user object, it creates confusion both for users and developers alike.

The Solution: Update Your Authentication Domain

After receiving feedback from Google Cloud support, it has been established that the issue stems from a mismatch between your Firebase authentication domain and your custom domain. This can cause new security features in browsers that block third-party cookies to disrupt the login flow.

Here’s How to Fix It

Follow these steps to resolve the null user state issue:

Update your Firebase auth configuration:

Change the authDomain value in your Firebase settings to match your custom domain. This ensures that your application recognizes the domain associated with the authentication request.

[[See Video to Reveal this Text or Code Snippet]]

Adjust the OAuth 2.0 Client ID Credentials:

Navigate to the API’s and Services console in Google Cloud.

Locate your OAuth 2.0 Client ID configuration.

In the redirect URLs section, add your new custom domain. It should look like this:

[[See Video to Reveal this Text or Code Snippet]]

Keep in mind, this redirect URL is distinct from the authorized domains found in the identity provider settings.

Final Thoughts

Implementing these changes should drastically improve the authentication flow within your application and reduce the instances of users encountering null states after successfully logging in.

Remember to always test login flows across different devices to ensure consistent behavior. By keeping your Firebase configurations aligned with your custom settings, you’re paving the way for a smoother user experience.

If you've encountered this issue or have other Firebase-related questions, feel free to share your experiences in the comments below!

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