Authenticating Android with firebase Authentication and send token to verify to backend Django

Question

The issue that I will address here is a pretty common, my concern is on one part of it that I will highlight:

My Android App authenticates users using firebase Authentication (either create or verify that exists), then calls various APIs on my django backend. To call APIs I need to send a token in each request so that I prevent unauthorized requests.

I was planning first of using Django Authentication, but since I am using firebase Auth, I'm thinking of the following approach:

When a user sign-in or log-in to Android device. The Android will generate a custom token (from firebase), store it on the phone and then send it in each API to the backend. In backend, I will use firebase API to get the user from firebase (the first time) and store the token in my users model. If the token is not found in my database and not available in firebase then I return a non-authorized user. For subsequent requests I validate the token with my local users table.

Please advise if this approach is the best in this case.

Thank you

Vivek Naik Vivek Naik · Accepted Answer · 2019-04-10T07:06:09

I can't comment about your approach. But even I want to know the best approach. Here is how I am doing it using the info provided in this page verify-id-tokens

User login using firebase sdk.

I attach the token as header in retrofit http call interceptor. Now the id token are only valid for 15-20 mins so you cant save them. Just use below code to add the interceptor in retrofit http call

public class FirebaseUserIdTokenInterceptor implements Interceptor {

// Custom header for passing ID token in request.
private static final String X_FIREBASE_ID_TOKEN = "Authorization";

@Override
public Response intercept(@NonNull Chain chain) throws IOException {
    Request request = chain.request();

    try {
        FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
        if (user == null) {
            throw new Exception("User is not logged in.");
        } else {
            Task<GetTokenResult> task = user.getIdToken(true);
            GetTokenResult tokenResult = Tasks.await(task);
            String idToken = tokenResult.getToken();

            if (idToken == null) {
                throw new Exception("idToken is null");
            } else {
                Request modifiedRequest = request.newBuilder()
                        .addHeader(X_FIREBASE_ID_TOKEN, "Bearer ".concat(idToken))
                        .build();
                return chain.proceed(modifiedRequest);
            }
        }
    } catch (Exception e) {
        throw new IOException(e.getMessage());
    }
}

}

My node server verifies the id token and response is sent if id token is valid else error message.

Check the warning on the page:

The ID token verification methods included in the Firebase Admin SDKs are meant to verify ID tokens that come from the client SDKs, not the custom tokens that you create with the Admin SDKs.

Hope this helps!!

Authenticating Android with firebase Authentication and send token to verify to backend Django

1 Answers