@Override
        public KafkaPrincipal principal() {
            InetAddress clientAddress = transportLayer.socketChannel().socket().getInetAddress();
            // listenerName should only be null in Client mode where principal() should not be called
            if (listenerName == null)
                throw new IllegalStateException("Unexpected call to principal() when listenerName is null");
            SslAuthenticationContext context = new SslAuthenticationContext(
                    transportLayer.sslSession(),
                    clientAddress,
                    listenerName.value());
            return principalBuilder.build(context);
        }
Constructs Principal using configured principalBuilder.
@return the built principal
clients/src/main/java/org/apache/kafka/common/network/SslChannelBuilder.java