code: private SecretKey clientKeyExchange(KerberosClientKeyExchange mesg)
          throws IOException {
  
          if (debug != null && Debug.isOn("handshake")) {
              mesg.print(System.out);
          }
  
          // Record the principals involved in exchange
          session.setPeerPrincipal(mesg.getPeerPrincipal());
          session.setLocalPrincipal(mesg.getLocalPrincipal());
  
          byte[] b = mesg.getUnencryptedPreMasterSecret();
          return new SecretKeySpec(b, "TlsPremasterSecret");
      }
docs: /*
  For Kerberos ciphers, the premaster secret is encrypted using
  the session key. See RFC 2712.