@Override
        public void close() throws IOException {
            defaultSslEngineFactory.close();
            closed = true;
        }
@param dn The distinguished name to use
@param keyPair A key pair to use
@param daysBeforeNow how many days before now the Certificate is valid for
@param daysAfterNow how many days from now the Certificate is valid for
@param issuer The issuer name. if null, "dn" is used
@param parentKeyPair The parent key pair used to sign this certificate. If null, create
       self-signed certificate authority (CA)
@return A (self-) signed certificate
@throws CertificateException
clients/src/test/java/org/apache/kafka/test/TestSslUtils.java