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This also introduces a new configuration that audit.extension.classes that allows to configure a comma separated list of Audit extension implementations. E.g.:

audit.extension.classes=org.apache.kafka.common.audit.LoggingAuditExtension,org.apache.kafka.common.audit.KafkaAuditExtension

Proposed Changes

Users will be able to create a plugin by implementing the AuditExtension interface that has a single method that takes an AuditEvent's children instance as the only parameter.
This allows us to change the interface easily in the future to add new parameters.
Audit runtime will also provide a default implementation for AuditEvent interface.
One or more of AuditExtension's implementations can be configured via the configuration audit.extension.classes as a comma separated list of class names.

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