KIP-425 adds SASL support to the Kafka Log4j appender however it does not include the improvements introduced with KIP-86. This KIP aims to do just that by exposing `sasl.login.callback.handler.class` for use by the appender's producer.
https://cwiki.apache.org/confluence/display/KAFKA/KIP-470%3A+Enable+KafkaLog4JAppender+to+use+SASL+Authentication+Callback+Handlers
