selfSigned.certificate,
        trusted.certificate,
      )
    assertThat(cleaner.clean(list(certB, certA), "hostname")).isEqualTo(
      list(certB, certA, trusted, selfSigned),
    )
    assertThat(cleaner.clean(list(certB, certA, trusted), "hostname")).isEqualTo(
      list(certB, certA, trusted, selfSigned),
    )
    assertThat(cleaner.clean(list(certB, certA, trusted, selfSigned), "hostname"))
      .isEqualTo(

/**
 * Certificates to identify which peers to trust and also to earn the trust of those peers in kind.
 * Client and server exchange these certificates during the handshake phase of a TLS connection.
 *
 * ### Server Authentication
 *
 * This is the most common form of TLS authentication: clients verify that servers are trusted and
 * that they own the hostnames that they represent. Server authentication is required.

   *
   *
   * The victim's gets a non-CA certificate signed by a CA, and pins the CA root and/or
   * intermediate. This is business as usual.
   *
   * ```
   *   pinnedRoot (trusted by CertificatePinner)
   *     -> pinnedIntermediate (trusted by CertificatePinner)
   *       -> realVictim
   * ```
   *
   * The attacker compromises a CA. They take the public key from an intermediate certificate

      val toVerify = result[result.size - 1] as X509Certificate

      // If this cert has been signed by a trusted cert, use that. Add the trusted certificate to
      // the end of the chain unless it's already present. (That would happen if the first
      // certificate in the chain is itself a self-signed and trusted CA certificate.)
      val trustedCert = trustRootIndex.findByIssuerAndSignature(toVerify)
      if (trustedCert != null) {

```

This handshake is successful because each party has prearranged to trust the root certificate that
signs the other party's chain.

Well-Known Certificate Authorities
----------------------------------

In these examples we've prearranged which root certificates to trust. But for regular HTTPS on the
Internet this set of trusted root certificates is usually provided by default by the host platform.

 * called certificate authorities (CAs).
 *
 * Browsers and other HTTP clients need a set of trusted root certificates to authenticate their
 * peers. Sets of root certificates are managed by either the HTTP client (like Firefox), or the
 * host platform (like Android). In July 2018 Android had 134 trusted root certificates for its HTTP
 * clients to trust.
 *
 * For example, in order to establish a secure connection to `https://www.squareup.com/`,

 * certificate is signed by the certificate that follows, and the last certificate is a trusted CA
 * certificate.
 *
 * Use of the chain cleaner is necessary to omit unexpected certificates that aren't relevant to
 * the TLS handshake and to extract the trusted CA certificate for the benefit of certificate
 * pinning.
 */
abstract class CertificateChainCleaner {

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

import java.security.cert.X509Certificate

fun interface TrustRootIndex {
  /** Returns the trusted CA certificate that signed [cert]. */
  fun findByIssuerAndSignature(cert: X509Certificate): X509Certificate?

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

import java.security.cert.X509Certificate
import javax.security.auth.x500.X500Principal

/** A simple index that of trusted root certificates that have been loaded into memory. */
class BasicTrustRootIndex(
  vararg caCerts: X509Certificate,
) : TrustRootIndex {
  private val subjectToCaCerts: Map<X500Principal, Set<X509Certificate>>

  init {

    version of the library.

5.  Our classes are not designed to protect against a malicious caller. You
    should not use them for communication between trusted and untrusted code.

6.  For the mainline flavor, we test the libraries using OpenJDK 8, 11, and 17
    on Linux, with some additional testing on newer JDKs and on Windows. Some