@Override
    public void configure(Map<String, ?> configs, String saslMechanism, List<AppConfigurationEntry> jaasConfigEntries) {
        this.mechanism  = saslMechanism;
    }
Default callback handler for Sasl clients. The callbacks required for the SASL mechanism
configured for the client should be supported by this callback handler. See
<a href="https://docs.oracle.com/javase/8/docs/technotes/guides/security/sasl/sasl-refguide.html">Java SASL API</a>
for the list of SASL callback handlers required for each SASL mechanism.

For adding custom SASL extensions, a {@link SaslExtensions} may be added to the subject's public credentials
clients/src/main/java/org/apache/kafka/common/security/authenticator/SaslClientCallbackHandler.java