Скачать или смотреть Understanding User.getIdToken() in Flutter Firebase Authentication: Caching vs. Server Queries

Explore whether `User.getIdToken()` queries the server every time in Flutter Firebase Authentication, and learn best practices for managing ID tokens efficiently.
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Understanding User.getIdToken() in Flutter Firebase Authentication: Caching vs. Server Queries

When developing applications with Flutter and Firebase, handling user authentication effectively is critical. One common question developers encounter is about the User.getIdToken() method: Does it query the server every time it's called? This inquiry is essential as it impacts app performance and server usage. Let’s break down this topic to understand how getIdToken() works, whether it caches tokens, and the best approach for managing ID tokens within your applications.

Does User.getIdToken() Query the Server Every Time?

The straightforward answer is no. When you call User.getIdToken() without forcing a refresh (i.e., with forceRefresh = false), it does not retrieve the ID token from the server each time you invoke it. Instead, it returns the last known value of the ID token which might already be cached.

How Token Caching Works

When getIdToken() is invoked without forceRefresh, the method relies on an automatically maintained cache.

The returned token may be freshly issued or may be an older value, depending on whether it has been refreshed recently.

This means that every time you call getIdToken(), it hands you back whatever the last known token is, rather than hitting the server for a new one.

Implications for Backend Requests

This leads to some important considerations when sending requests to your app’s backend server. If you are concerned about having to contact the Firebase server continually for an ID token, rest assured there are mechanisms in place to manage this efficiently.

The Persistent Token Issue

If getIdToken() were to query for a new token every time you needed one, it could lead to significant overhead, especially if your app frequently sends requests to the backend. Fortunately, Firebase’s design circumvents this:

Token Caching: By default, the SDK caches the token, so you do not have to reach out to Firebase for each backend request.

Custom Caching: While Firebase handles the basic caching, you can also implement your own logic to store the token and track its validity. This is useful if you want more control over when to refresh your tokens or if you want to reduce calls to the Firebase server.

Recommended Practices for Token Management

Though the convenience of not querying the server every time is a significant advantage, developers need to stay updated on token validity. Here are some recommended practices:

1. Listen to Token Changes

While you expressed hesitance to use idTokenChanges which could lead to unnecessary UI rebuilding:

It is generally the recommended approach because it keeps your ID token fresh automatically.

Firebase handles refreshing the token in the background, so your app can operate smoothly without manual intervention.

2. Use authStateChanges Stream

If you prefer to rebuild the UI only during sign-in or sign-out events:

You can listen to authStateChanges which will notify your app of any changes in authentication state.

Be aware that you will still need to manage token freshness manually in this scenario when sending requests to your backend.

3. Optimize Backend Calls

To prevent unnecessary server hits:

Cache the ID token in your app and monitor its expiry time.

Only request a fresh token if you’re aware that it has expired or on events that require validation.

Conclusion

In conclusion, User.getIdToken() does not query Firebase every time it’s called unless you explicitly request it to refresh. It returns the last available token value, which can dramatically reduce the number of requests to the server. Understanding how to manage token caching and im