// sufficient to connect to most HTTPS sites including https://godaddy.com and https://visa.com.
  // Typically developers will need to get a PEM file from their organization's TLS administrator.
  final X509Certificate comodoRsaCertificationAuthority = Certificates.decodeCertificatePem(""
      + "-----BEGIN CERTIFICATE-----\n"

import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;

/**
 * Fetches HTML from a requested URL, follows the links, and repeats.
 */
public final class Crawler {
  private final OkHttpClient client;
  private final Set<HttpUrl> fetchedUrls = Collections.synchronizedSet(new LinkedHashSet<>());