Understanding the context.auth Field in Firebase Cloud Functions for Firestore

Описание: A comprehensive guide on how to handle user authentication in Firebase Cloud Functions for Firestore, including the limitations of the `context.auth` field and a suggested workaround.
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This video is based on the question https://stackoverflow.com/q/68800305/ asked by the user 'Max Gusenbauer' ( https://stackoverflow.com/u/7937665/ ) and on the answer https://stackoverflow.com/a/68800682/ provided by the user 'Renaud Tarnec' ( https://stackoverflow.com/u/3371862/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Does the context.auth Field Work for Firestore Cloud Functions?

If you're working with Firebase Cloud Functions and Firestore, you might be wondering about the functionality of the context.auth field. Specifically, does it allow you to retrieve the user ID (uid) of the person who triggered the function? This question has generated a lot of confusion, with varying responses in different forums. In this post, we'll clarify the issue and provide you with a practical solution.

The Limitations of context.auth for Firestore

Key Points to Consider

The context.auth field does not work with Firestore Cloud Functions.

When you use Firestore as your database, the context parameter in the function does not contain any authentication information about the user who triggered the function.

Example of the Issue

Let's take a look at a typical Firestore Cloud Function:

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

In this example, you would expect to retrieve the user's uid from context.auth. However, in practice, context.auth will often return undefined. This can be frustrating, especially when you need to track which user initiated specific changes to your Firestore documents.

What You Can Do Instead

While the inability to access context.auth directly can be limiting, there are still ways to authenticate users securely. Here’s how you can work around this challenge:

Workaround: Store User UID in Firestore

Add uid to Firestore Documents:
When users interact with your Firestore database, ensure that you store their uid in the documents they are updating or creating. For instance, you could have a field named userId in each document that corresponds to the authenticated user's id.

Implement Security Rules:
To enhance security, you should write Firestore security rules that validate that the userId in the document matches the uid of the authenticated user. For example:

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

This way, even though you cannot retrieve context.auth information directly, you can still ensure that users are only making changes to documents they own.

Conclusion

In conclusion, while the context.auth field does not provide the user UID in Firestore Cloud Functions, you can utilize a workaround that includes storing the UID in the Firestore documents and setting up appropriate security rules. This approach maintains a secure environment while enabling you to track user interactions effectively. If you have any further questions or need assistance with your Firebase project, feel free to reach out!