This is a Java plugin for Logstash.
It is fully free and fully open source. The license is Apache 2.0, meaning you are free to use it however you want.
The documentation for Logstash Java plugins is available here.
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NOTE: Needs java 11 jdk, along with the logstash product which is needed to build; at least 'gradlew assemble' to make the logstash-core.jar