ClassNotFoundException exception occurred: io.confluent.kafka.security.config.provider.SecurePassConfigProvider (kafka.server.KafkaConfig)

The community edition of Confluent Platform 5.5.2 does not come with this class...

$ find ./confluent-5.5.2 -name 'kafka-client-plugins*.jar'

Download the file here and make sure it is in the Kafka broker classpath, e.g. /usr/share/java/kafka if installed directly to the OS, or the share/java/kafka folder of the Confluent tarball.

https://packages.confluent.io/maven/io/confluent/kafka-client-plugins/5.5.2-ce/kafka-client-plugins-5.5.2-ce.jar

Verified with

$ jar -tf kafka-client-plugins-5.5.2-ce.jar| grep SecurePassConfigProvider
io/confluent/kafka/security/config/provider/SecurePassConfigProvider.class

Overall, if someone has file-system access to your brokers, you have bigger problems, and obscuring the file with a direct reference to another is not "secure"