Chapter 12. KafkaListenerAuthenticationCustom schema reference

Listener configuration specified using listenerConfig is prefixed with listener.name.<listener_name>-<port>. For example, sasl.enabled.mechanisms becomes listener.name.<listener_name>-<port>.sasl.enabled.mechanisms.

Secrets are mounted to /opt/kafka/custom-authn-secrets/custom-listener-<listener_name>-<port>/<secret_name> in the Kafka broker nodes' containers.

For example, the mounted secret (example) in the example configuration would be located at /opt/kafka/custom-authn-secrets/custom-listener-oauth-bespoke-9093/example.

You can set a custom principal builder in the Kafka cluster configuration. However, the principal builder is subject to the following requirements:

Custom principal builders must support peer certificates for authentication, as Streams for Apache Kafka uses these to manage the Kafka cluster.

The following example shows a custom principal builder that satisfies the OAuth requirements of Streams for Apache Kafka.

public final class CustomKafkaPrincipalBuilder implements KafkaPrincipalBuilder {

    public KafkaPrincipalBuilder() {}

    @Override
    public KafkaPrincipal build(AuthenticationContext context) {
        if (context instanceof SslAuthenticationContext) {
            SSLSession sslSession = ((SslAuthenticationContext) context).session();
            try {
                return new KafkaPrincipal(
                    KafkaPrincipal.USER_TYPE, sslSession.getPeerPrincipal().getName());
            } catch (SSLPeerUnverifiedException e) {
                throw new IllegalArgumentException("Cannot use an unverified peer for authentication", e);
            }
        }

        // Create your own KafkaPrincipal here
        ...
    }
}

The type property is a discriminator that distinguishes use of the KafkaListenerAuthenticationCustom type from KafkaListenerAuthenticationTls, KafkaListenerAuthenticationScramSha512, KafkaListenerAuthenticationOAuth. It must have the value custom for the type KafkaListenerAuthenticationCustom.