val data = CertificateAdapters.certificate.toDer(this)
    try {
      val certificateFactory = CertificateFactory.getInstance("X.509")
      val certificates = certificateFactory.generateCertificates(Buffer().write(data).inputStream())
      return certificates.single() as X509Certificate
    } catch (e: NoSuchElementException) {
      throw IllegalArgumentException("failed to decode certificate", e)
    } catch (e: IllegalArgumentException) {

    val certificate = heldCertificate.certificate
    assertThat(certificate.getSubjectX500Principal().name, "self-signed")
      .isEqualTo(certificate.getIssuerX500Principal().name)
    assertThat(certificate.getIssuerX500Principal().name).matches(Regex("CN=[0-9a-f-]{36}"))
    assertThat(certificate.serialNumber).isEqualTo(BigInteger.ONE)
    assertThat(certificate.subjectAlternativeNames).isNull()

import okhttp3.OkHttpClient;
import okhttp3.Protocol;
import okhttp3.Request;
import okhttp3.Response;
import org.junit.Test;
import org.junit.runner.RunWith;

import java.io.IOException;
import java.security.cert.Certificate;
import java.security.cert.X509Certificate;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

/**
 * Simple test adaptable to show a failure in older versions of OkHttp

import okhttp3.mockwebserver.MockResponse;
import okhttp3.mockwebserver.MockWebServer;
import okhttp3.tls.HandshakeCertificates;
import okhttp3.tls.HeldCertificate;

/**
 * Create an HTTPS server with a self-signed certificate that OkHttp trusts.
 */
public class HttpsServer {
  public void run() throws Exception {
    HeldCertificate localhostCertificate = new HeldCertificate.Builder()
        .addSubjectAlternativeName("localhost")

## Version 4.2.0

_2019-09-10_

 *  New: API to decode a certificate and private key to create a `HeldCertificate`. This accepts a
    string containing both a certificate and PKCS #8-encoded private key.

    ```kotlin
    val heldCertificate = HeldCertificate.decode("""
        |-----BEGIN CERTIFICATE-----
        |MIIBYTCCAQegAwIBAgIBKjAKBggqhkjOPQQDAjApMRQwEgYDVQQLEwtlbmdpbmVl

        .build()
    val handshakeCertificates =
      HandshakeCertificates.Builder()
        .heldCertificate(heldCertificate)
        .addTrustedCertificate(heldCertificate.certificate)
        .build()
    server.useHttps(handshakeCertificates.sslSocketFactory())

    val dns =
      Dns {
        Dns.SYSTEM.lookup(server.hostName)
      }

    val client =

    if (routes == null || !routeMatchesAny(routes)) return false

    // 3. This connection's server certificate's must cover the new host.
    if (address.hostnameVerifier !== OkHostnameVerifier) return false
    if (!supportsUrl(address.url)) return false

    // 4. Certificate pinning must match the host.
    try {
      address.certificatePinner!!.check(address.url.host, handshake()!!.peerCertificates)

        .build()
    val handshakeCertificates =
      HandshakeCertificates.Builder()
        .heldCertificate(heldCertificate)
        .addTrustedCertificate(heldCertificate.certificate)
        .build()

    client =
      client.newBuilder()
        .sslSocketFactory(
          handshakeCertificates.sslSocketFactory(),
          handshakeCertificates.trustManager,
        )

 * limitations under the License.
 */
package okhttp3.tls.internal.der

import okio.Buffer
import okio.ByteString

/**
 * Encode and decode a model object like a [Long] or [Certificate] as DER bytes.
 */
internal interface DerAdapter<T> {
  /** Returns true if this adapter can read [header] in a choice. */
  fun matches(header: DerHeader): Boolean

  /**
   * Returns a value from this adapter.

    }

    private fun certificatesToString(certificates: Array<X509Certificate>): String {
      val result: MutableList<String> = ArrayList()
      for (certificate in certificates) {
        result.add(certificate.subjectDN.toString() + " " + certificate.serialNumber)
      }
      return result.toString()
    }
  }

  /**