How can I create custom headers/or add metadata for messages a producer generates and access the header/metadata on the consumer side

[iec-1]

I want to add a few strings in every message/event. The rd_kafka_producev function takes a RD_KAFKA_VTYPE_OPAQUE can I use that to add my custom metadata/header? I also see RD_KAFKA_VTYPE_HEADER and RD_KAFKA_VTYPE_HEADERS.. Can I use one of those or is there another way? Also, how do i access my custom header/metadata using the rd_kafka_consumer_poll? I was reading the documentation on the rd_kafka_message_t, which is the return type, for rd_kafka_consumer_poll and it states the the opaque pointer should not be used on the consumer side. Looking for the correct approach and functions to use. Thanks.