code: private Map<String, List<String>> systemDefaultAuthentication(Route route, Request request, Response response) {
          InetSocketAddress proxyAddress = (InetSocketAddress) route.getProxy().address();
          String host = proxyAddress.getHostString();
          InetAddress addr = proxyAddress.getAddress();
          int port = proxyAddress.getPort();
          URL url = route.getUrl();
          String protocol = url.getProtocol();
  
          return response.getChallenges("basic")
                  .filter(challenge -> challenge.getRealm().isPresent())
                  .filter(challenge -> {
                      String charset = challenge.getAuthParams().get("charset");
                      return charset == null || charset.equalsIgnoreCase("UTF-8");
                  })
                  .map(challenge -> {
                      String realm = challenge.getRealm().orElseThrow(AssertionError::new);
                      PasswordAuthentication passwordAuthentication =
                              java.net.Authenticator.requestPasswordAuthentication(host, addr, port, protocol,
                                      realm, challenge.getScheme(), url, java.net.Authenticator.RequestorType.PROXY);
                      if (passwordAuthentication != null) {
                          Charset charset = challenge.getAuthParams().containsKey("charset")
                                  ? StandardCharsets.UTF_8
                                  : StandardCharsets.ISO_8859_1;
                          return Credentials.basic(passwordAuthentication.getUserName(),
                                  String.valueOf(passwordAuthentication.getPassword()), charset);
                      }
                      return null;
                  })
                  .filter(Objects::nonNull)
                  .filter(credentials ->
                          request.getHeaders("Proxy-Authorization").stream().noneMatch(credentials::equals))
                  .findAny()
                  .map(credentials -> Collections.singletonMap("Proxy-Authorization", Arrays.asList(null, credentials)))
                  .orElse(null);
      }
docs: Generates a {@code Basic} auth header with credentials from the system default authenticator.
  
  @param route    The route to which a request is done that needs to be authenticated.
  @param request  The originating request that led to the authentication attempt.
  @param response The response that demands authentication.
  @return The {@code Basic} auth header.