Envelope envelope = Envelope.defineSchema()
        .withName("event.Envelope")
        .withRecord(recordSchema)
        .withSource(SchemaBuilder.struct().build())
        .build();

final Struct before = new Struct(recordSchema);
before.put("id", eventId);
before.put("aggregatetype", payloadType);
before.put("aggregateid", payloadId);
before.put("type", eventType);
before.put("payload", payload);

extraValues.forEach(before::put);

final Struct body = envelope.create(before, null, Instant.now());