to generate a trusted root certificate, an intermediate certificate, and a server certificate.
We use `certificateAuthority(int)` to create certificates that can sign other certificates. The
int specifies how many intermediate certificates are allowed beneath it in the chain.

```java
HeldCertificate rootCertificate = new HeldCertificate.Builder()
    .certificateAuthority(1)
    .build();

     * certificate can sign other certificates (but those certificates cannot themselves sign
     * certificates). Set this to 1 so this certificate can sign intermediate certificates that can
     * themselves sign certificates. Add one for each additional layer of intermediates to permit.
     */
    fun certificateAuthority(maxIntermediateCas: Int) =
      apply {

    // Add a bad intermediate CA and have that issue a rogue certificate for localhost. Prepare
    // an SSL context for an attacking webserver. It includes both these rogue certificates plus the
    // trusted good certificate above. The attack is that by including the good certificate in the
    // chain, we may trick the certificate pinner into accepting the rouge certificate.
    val compromisedIntermediateCa =
      HeldCertificate

      }
    }

  fun verify(
    host: String,
    certificate: X509Certificate,
  ): Boolean =
    when {
      host.canParseAsIpAddress() -> verifyIpAddress(host, certificate)
      else -> verifyHostname(host, certificate)
    }

  /** Returns true if [certificate] matches [ipAddress]. */
  private fun verifyIpAddress(
    ipAddress: String,
    certificate: X509Certificate,
  ): Boolean {

Before Let's Encrypt, these **HTTPS certificates** were sold by trusted third parties.

The process to acquire one of these certificates used to be cumbersome, require quite some paperwork and the certificates were quite expensive.

But then **[Let's Encrypt](https://letsencrypt.org/)** was created.

@file:Suppress("DEPRECATION")

package okhttp3

import java.security.Principal
import java.security.cert.Certificate
import javax.net.ssl.SSLPeerUnverifiedException
import javax.net.ssl.SSLSession
import javax.net.ssl.SSLSessionContext
import javax.security.cert.X509Certificate

class FakeSSLSession(
  vararg val certificates: Certificate,
) : SSLSession {
  override fun getApplicationBufferSize(): Int = throw UnsupportedOperationException()

        )
      },
    )

  /**
   * ```
   * Certificate ::= SEQUENCE  {
   *   tbsCertificate       TBSCertificate,
   *   signatureAlgorithm   AlgorithmIdentifier,
   *   signatureValue       BIT STRING
   * }
   * ```
   */
  internal val certificate: BasicDerAdapter<Certificate> =
    Adapters.sequence(
      "Certificate",
      tbsCertificate,
      algorithmIdentifier,

import okhttp3.Request
import okhttp3.tls.HandshakeCertificates
import okhttp3.tls.decodeCertificatePem
import org.junit.jupiter.api.Tag
import org.junit.jupiter.api.Test

/**
 * Test for new Let's Encrypt Root Certificate.
 */
@Tag("Remote")
class LetsEncryptClientTest {
  @Test fun get() {
    // These tests wont actually run before Android 8.0 as per
    // https://github.com/mannodermaus/android-junit5

    assertThat(listOf(clientCertificate.certificate, clientIntermediate.certificate))
      .isEqualTo(serverHandshake.peerCertificates)
    assertThat(listOf(serverCertificate.certificate, serverIntermediate.certificate))
      .isEqualTo(serverHandshake.localCertificates)
    val clientHandshake = clientHandshakeFuture.get()
    assertThat(listOf(serverCertificate.certificate, serverIntermediate.certificate))

    val certificate: X509Certificate = heldCertificate.certificate
    val certificatePinner: CertificatePinner = CertificatePinner.Builder().build()
    val certificates: List<Certificate> = listOf()
    certificatePinner.check("", listOf(certificate))
    certificatePinner.check("", arrayOf<Certificate>(certificate, certificate).toList())
    val pin: String = CertificatePinner.pin(certificate)