ClientInterceptor and Firebase IdToken

[developerGM]

Hi, I am usign GRPC service and I am trying to extends ClientInterceptor to append some headers and ask to Firebase to give me a IdToken but I don't understand how can do it because task.getResult() go to in exception java.lang.IllegalStateException: Task is not yet complete

I have tried also with a sync mode
GetTokenResult tokenResult = Tasks.await(task, 20, TimeUnit.SECONDS);
but nothing, exception java.lang.IllegalStateException: Must not be called on the main application thread

public class CustomHeaderInterceptor implements ClientInterceptor {
    @Override
    public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
        return new ForwardingClientCall.SimpleForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
            @Override
            public void start(Listener<RespT> responseListener, Metadata headers) {
                headers.put(Metadata.Key.of("X-XXX", Metadata.ASCII_STRING_MARSHALLER), "test_test");

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

                        String idToken = tokenResult.getToken();
                        headers.put(Metadata.Key.of("Authorization", Metadata.ASCII_STRING_MARSHALLER), "Bearer " + idToken);

                        super.start(responseListener, headers);
                    }
                } catch (Exception e) {
                    Log.d(this.getClass().getName(), new Gson().toJson(e));
                }
            }
        };
    }
}

I have tried also CompletableFuture

                        Task<GetTokenResult> task = user.getIdToken(false);
                        CompletableFuture<String> completableFuture = new CompletableFuture<>();
                        task.addOnCompleteListener(new OnCompleteListener<>() {
                           @Override
                            public void onComplete(Task<GetTokenResult> task1) {
                                GetTokenResult tokenResult = task1.getResult();
                                String idToken = tokenResult.getToken();
                                completableFuture.complete(idToken);
                           }
                        });
                        String idToken = completableFuture.get();

but the code stop on completableFuture.get()

How can I do to ask and append on each call the firebase token?

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[bhparijat]

Hi,
Could you just try

String idToken = null;
Task<GetTokenResult> task = user.getIdToken(false);
                        
                        task.addOnCompleteListener(new OnCompleteListener<>() {
                           @Override
                            public void onComplete(Task<GetTokenResult> task1) {
                                GetTokenResult tokenResult = task1.getResult();
                                idToken = tokenResult.getToken();
                               
                           }
                        });
                        

and let us know if it works.

[developerGM]

I can't use this code because is an async procedure and ClientInterceptor don't wait onComplete to continue

[argzdev]

Hi @developerGM, in Retrofit interceptors using Kotlin we can use coroutines that would help solve this issue. As an example, I used an Interceptor in Retrofit, I imagine this would be somewhat similar to the interceptor you're using for gRPC. In Kotlin, we can just use the runBlocking wrapper to create a synchronous call:

class AuthenticationInterceptor() : Interceptor {
    @Throws(IOException::class)
    override fun intercept(chain: Interceptor.Chain): Response {
        val authToken = runBlocking {
            val token = Firebase.auth.currentUser?.getIdToken(false)?.await()?.token ?: return@runBlocking ""
            return@runBlocking token
        }

        val original: Request = chain.request()
        val builder: Request.Builder = original.newBuilder().header("Authorization", authToken)
        val request: Request = builder.build()
        return chain.proceed(request)
    }
}

I'm not sure what the equivalent of runBlocking in Java. I'd recommend you to post this in community channels such as Stack Overflow, I'm sure they'll be able to help you better.

However, please do note that this approach is also somewhat discouraged. I'd advise you to try the recommend approach which is:

Their recommendation is to handle this outside OkHttp, so in your case to first fetch the token in an async way and then initiate the HTTP request.

This way, your approach would be fetching the token on app launch and store it for the current session, and then do http requests whenever necessary with the stored token.

That said, unfortunately I'm not sure if there's anyway else we can help you with this, since this looks more of a code problem than a SDK issue. I'll close this thread for now. If you feel that this is a mistake, let us know and we'll reopen this again. Thanks!

[argzdev]

Hi @developerGM, after further discussions, we've decided to reopen this as a feature request instead. It'll be beneficial for our future developers if we have a proper documentation regarding how to use Firebase Authentication with gRPC. Thanks!

[developerGM]

Ok, thanks