Cloudflare protection. (TypeError: Cannot find function observe.)

[FurfurDev]

Hello, I'm trying to download a jar file from the website www.spigotmc.org , but I'm having trouble getting through Cloudflare's protection

My code:

import org.htmlunit.CookieManager;
import org.htmlunit.NicelyResynchronizingAjaxController;
import org.htmlunit.WebClient;
import org.htmlunit.html.HtmlPage;
import org.junit.jupiter.api.Test;

public class NetworksUtilTest
{
    private static final WebClient webClient = new WebClient();

    @Test
    void htmlUnitTest() throws Exception
    {
        webClient.addRequestHeader("Connection", "keep-alive");
        webClient.addRequestHeader("Upgrade-Insecure-Requests", "1");
        webClient.addRequestHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.86 Safari/537.36");
        webClient.addRequestHeader("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8");
        webClient.addRequestHeader("Accept-Language", "en-US,en;q=0.9");
        webClient.addRequestHeader("Accept-Encoding", "gzip, deflate");

        webClient.getOptions().setThrowExceptionOnFailingStatusCode(false);
        webClient.getOptions().setThrowExceptionOnScriptError(false);
        webClient.getOptions().setFetchPolyfillEnabled(true);
        webClient.getOptions().setPopupBlockerEnabled(true);
	    webClient.getOptions().setGeolocationEnabled(false);
        webClient.getOptions().setJavaScriptEnabled(true);
        webClient.getOptions().setDoNotTrackEnabled(true);
        webClient.getOptions().setRedirectEnabled(true);
        webClient.getOptions().setDownloadImages(false);
        webClient.getOptions().setUseInsecureSSL(true);
        webClient.getOptions().setScreenHeight(768);
        webClient.getOptions().setScreenWidth(1366);
        webClient.getOptions().setCssEnabled(false);
	    webClient.getOptions().setTimeout(5000);

        CookieManager cookieManager = new CookieManager();
        webClient.setCookieManager(cookieManager);

        webClient.setAjaxController(new NicelyResynchronizingAjaxController());
        webClient.setAlertHandler((page, message) -> System.err.println("[alert] " + message)); // to be changed
        webClient.setJavaScriptTimeout(5000);
        webClient.getCookieManager().setCookiesEnabled(true);
        webClient.getCache().setMaxSize(1);

        HtmlPage htmlCloudflarePage = webClient.getPage("https://www.spigotmc.org/resources/vault.34315/download?version=344916");
        webClient.waitForBackgroundJavaScript(5_000);
        System.out.println(htmlCloudflarePage.getWebResponse().getResponseHeaderValue("Content-Type"));

        webClient.close();
    }
}

logs: log.txt

Gradle Version: gradle-9.5.1
HtmlUnit Version: 5.1.0

Update (10.08.2026)

XML Response: cloudflare.xml

[rbri]

Currently on vacation, will have a look next week...