String stateString = requestUrl.queryParameter("state");
    ByteString state = stateString != null ? ByteString.decodeBase64(stateString) : null;

    Listener listener;
    synchronized (this) {
      listener = listeners.get(state);
    }

    if (code == null || listener == null) {
      return new MockResponse()
          .setResponseCode(404)
          .setBody("unexpected request");
    }

    if (previous != null) hostnameCount = previous;
    if (hostnameCount.incrementAndGet() > 100) return;

    Request request = new Request.Builder()
        .url(url)
        .build();
    try (Response response = client.newCall(request).execute()) {
      String responseSource = response.networkResponse() != null ? ("(network: "
          + response.networkResponse().code()

    System.out.println("MESSAGE: " + bytes.hex());
  }

  @Override public void onClosing(WebSocket webSocket, int code, String reason) {
    webSocket.close(1000, null);
    System.out.println("CLOSE: " + code + " " + reason);
  }

  @Override public void onFailure(WebSocket webSocket, Throwable t, Response response) {
    t.printStackTrace();
  }

  private final OkHttpClient client;

  public Authenticate() {
    client = new OkHttpClient.Builder()
        .authenticator((route, response) -> {
          if (response.request().header("Authorization") != null) {
            return null; // Give up, we've already attempted to authenticate.
          }

          System.out.println("Authenticating for response: " + response);
          System.out.println("Challenges: " + response.challenges());