Why are my Firebase ID tokens failing Identity Platform validation on Cloud Run?

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I'm using Firebase Authentication ID tokens in my React Native (Expo) frontend and sending them in the Authorization header of requests to my Google Cloud Run backend via a Cloud Load Balancer. However, when I configure Cloud Run to require authentication (by granting the allAuthenticatedUsers role), all requests get a 401 error, even though direct invocation works when I assign the roles/run.invoker role to allUsers.

I create and send the token as follows:

JAVASCRIPT
const userCredential = await signInWithEmailAndPassword(auth, email, password);
const idToken = await userCredential.user.getIdToken();

Then I include it in my request headers:

JAVASCRIPT
headers: {
    'Content-Type': 'application/json',
    Authorization: `Bearer ${idToken}`,
}

Details I've checked:

My Cloud Run service requires authentication, and I’ve set a custom audience using my Google Cloud project ID (which matches the token’s aud claim).
The token’s iss value is https://securetoken.google.com/my-project-id.
I verified the token in my backend code using Firebase Admin SDK, but Cloud Run still rejects it at the platform level.

I suspect one of the following may be the issue:

The custom audience for Cloud Run doesn’t exactly match the token's aud claim.
The load balancer or Cloud Armor might be stripping or modifying the Authorization header.
There might be a mismatch between how Firebase tokens and Cloud Run Authentication (via Identity Platform) are expected to work.

Is it possible to have Firebase Authentication ID tokens work at the platform level with Identity Platform, and if so, what might I be doing wrong? Any insights would be appreciated!

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

Below is an explanation and some troubleshooting ideas based on Identity Platform and Firebase Authentication documentation:

Can Firebase ID Tokens Work with Identity Platform?

Yes. Firebase Authentication ID tokens are issued from the same backend (Identity Platform) that supports end user authentication. In other words, the tokens you generate on your React Native app can work with Cloud Run when you configure authentication correctly.

Things to Check and Troubleshoot

Audience (aud) Claim:
Your Firebase ID token has an "aud" claim equal to your project ID. Cloud Run expects the token’s audience to match its configuration. When using Cloud Run with Identity Platform authentication, you typically need to add your project ID as a custom audience. Double-check that the custom audience setting on your Cloud Run service exactly matches the "aud" value in your Firebase token.
Issuer (iss) Claim:
Your token’s issuer is https://securetoken.google.com/my-project-id, which is correct for Firebase tokens. Cloud Run’s validation will check that the token comes from this issuer.
Authentication Flow Through the Load Balancer:
Since you’re routing requests through a load balancer with Cloud Armor, ensure that the LB is preserving the Authorization header. Any misconfiguration in the load balancer or Cloud Armor rules might remove or alter the header before it reaches your Cloud Run service.
Roles Configuration:
You mentioned that granting allUsers the roles/run.invoker role works but isn’t acceptable because you want to restrict it to authenticated users. When you switch to using allAuthenticatedUsers, Cloud Run expects a token validated by Identity Platform. Make sure that the token you send is not only passing the Authorization header but is being recognized as valid by Cloud Run’s built‐in authentication.
Token Propagation and Verification:
Even though you can verify the token in your backend code using the Firebase Admin SDK, Cloud Run’s front door (the authentication layer) performs its own validation. Sometimes tokens might pass your application verification but fail the platform-level check if the audience or issuer isn’t configured as expected.

Next Steps

Verify Your Custom Audience: Confirm that the custom audience for your Cloud Run service exactly matches the project ID in the token’s "aud" claim.
Examine Load Balancer Configuration: Make sure that the load balancer (and any proxy or Cloud Armor rule) isn’t stripping or modifying the Authorization header.
Test Direct Invocation: As a sanity check, try sending a request directly to the Cloud Run URL (bypassing the load balancer) with the Firebase ID token in the header. If it works, then the issue lies with the routing configuration.

By ensuring the token's audience, issuer, and proper header propagation, Firebase Authentication ID tokens should work seamlessly with Identity Platform at the platform level for your Cloud Run service.

Hope this helps!

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by JovianTraveler168 • 1 month ago

can Firebase Authentication idToken's even work with Identity Platform at the platform level?

No, they can't. Firebase Authentication user ID tokens are JWTs that are meant to be decoded using the Firebase Admin SDK as described in the documentation. These tokens have no meaning as GCP IAM identities or roles. They are only useful to code and other Firebase services (such as Firebase security rules) that are designed specifically to use them.

When you use the GCP IAM allUsers role, that allows access to some GCP resource without any tokens provided at all. That explains why your Firebase token appears to be valid and useful, when in actuality, it is not.

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Why are my Firebase ID tokens failing Identity Platform validation on Cloud Run?

2 Answers

Can Firebase ID Tokens Work with Identity Platform?

Things to Check and Troubleshoot

Next Steps

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