HAProxy as a forward proxy for FCM admin SDK

Help!
1

I have a case in my setup which requires to connect from my app server to FCM since this is not allowed directly from app server and I already have HAProxy so I’m planning to use it as a forward proxy, FCM admin SDK support this via configuration where I can configure HAProxy as a proxy when I put IP and and Port I made already those changes in SDK

Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(HAProxy_hostname,HAProxy_port));
            HttpTransport httpTransport = new NetHttpTransport.Builder()
                    .setProxy(proxy)
                    .build();

            GoogleCredentials googleCredentials = GoogleCredentials.fromStream(googleCredentialsConfigurationStream,() -> httpTransport);
            FirebaseOptions firebaseOptions = FirebaseOptions
                    .builder()
                    .setHttpTransport(httpTransport)
                    .setCredentials(googleCredentials)
                    .build();

            FirebaseApp.initializeApp(firebaseOptions);

Also applied some configuration on HAProxy side as below, but I got an error related to following Unknown error while making a remote service call: Error getting access token for service account: Unexpected end of file from server, iss: firebase-adminsdk-2653537

frontend fcmproxy_frontend
        bind    *:8084 transparent
        #stats   uri /haproxy?stats
        default_backend         fcm_backend
        mode    tcp
        option  tcplog
        tcp-request content accept if HTTP
        tcp-request inspect-delay 10s
backend fcm_backend
        mode    tcp
        timeout tunnel  3000s
        server          FCM     aws.com verify none #dummy URL since server is not used in this case instead it should use request hostname

Can you spot in any of the errors in the following configuration ?