Currently, I am using the Firebase Admin SDK to send Firebase messages in a Java server-side application.

I can send messages without a proxy and through a proxy without basic authentication.

However, when I try to send a message through a proxy with basic authentication, it fails with a 407 error.

Here is my code

      String proxy_addr = "my_proxy_addr";
      int proxy_port = my_proxy_port;
      String proxy_name = "my_proxy_name";
      String proxy_pass = "my_proxy_password";
      String file_path = "my_auth_file_path";

      System.setProperty("https.proxyHost", proxy_addr);
      System.setProperty("https.proxyPort", String.valueOf(proxy_port));
      System.setProperty("jdk.http.auth.tunneling.disabledSchemes", "");

      Authenticator.setDefault(new Authenticator() {
         @Override
         protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(proxy_name, proxy_pass.toCharArray());
         }
      });

      Proxy proxy  = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(proxy_addr, proxy_port));
      HttpTransport transport = new NetHttpTransport.Builder().setProxy(proxy).build();
 
      HttpTransportFactory httpTransportFactory = new HttpTransportFactory() {
         @Override
         public HttpTransport create() {
           return transport;
         }
      };

      FileInputStream stream = new FileInputStream(file_path);
      GoogleCredentials googleCredentials = GoogleCredentials.fromStream(stream, httpTransportFactory);
      FirebaseOptions options = FirebaseOptions.builder()
          .setCredentials(googleCredentials)
          .setHttpTransport(transport)
          .build();
      FirebaseApp.initializeApp(options);

      FirebaseMessaging.getInstance().sendMulticast(message);

What am I doing wrong ?