How to integrate firebase authentication with google app engine endpoints

Question

I am writing a backend server for mobile applications. The backend is running on google app engine and written in Java.

I want users to be able to login with federated i

Answer 1

You should be able to use Google Cloud Endpoints as an authentication proxy in front of your app. Endpoints supports validating Firebase Authentication tokens by configuring your OpenAPI template:

# Configure Firebase as an AuthN provider
securityDefinitions:
    firebase:
      authorizationUrl: ""
      flow: "implicit"
      type: "oauth2"
      # Replace YOUR-PROJECT-ID with your project ID in the issuer and audiences fields
      x-google-issuer: "https://securetoken.google.com/YOUR-PROJECT-ID"
      x-google-audiences: "YOUR-PROJECT-ID"
      x-google-jwks_uri: "https://www.googleapis.com/service_accounts/v1/metadata/x509/securetoken@system.gserviceaccount.com"

# Add Firebase as an authN provider to specific endpoints...
security:
  - firebase: []

Alternatively, you can use the Firebase Admin SDK to write authentication middleware that validates your tokens:

FirebaseAuth.getInstance().verifyIdToken(idToken)
    .addOnSuccessListener(new OnSuccessListener() {
        @Override
        public void onSuccess(FirebaseToken decodedToken) {
            String uid = decodedToken.getUid();
            // ...
        }
});