`HandshakeCertificates` holds the TLS certificates required for a TLS handshake. On the server
    it keeps your `HeldCertificate` and its chain. On the client it keeps the root certificates
    that are trusted to sign a server's certificate chain. `HandshakeCertificates` also works with
    mutual TLS where these roles are reversed.

    These classes make it possible to enable HTTPS in MockWebServer in [just a few lines of

          this.routeDatabase = null
        }

        this.hostnameVerifier = hostnameVerifier
      }

    /**
     * Sets the certificate pinner that constrains which certificates are trusted. By default HTTPS
     * connections rely on only the [SSL socket factory][sslSocketFactory] to establish trust.
     * Pinning certificates avoids the need to trust certificate authorities.
     */