The v5 native protocol spec currently only supports custom payloads on query execution messages: https://github.com/apache/cassandra/blob/61b3d5a54befe440044ad86159a62fee487229eb/doc/native_protocol_v5.spec#L297-L298
> Currently, only QUERY, PREPARE, EXECUTE and BATCH requests support custom > payloads. The Java driver also does not log warnings if they’re provided on other response message types, even though this is compliant with the spec. Any objections to relaxing this restriction, so we can expose warnings and custom payloads for other protocol messages, like the authentication flow? This is especially relevant with CEP-50: Authentication Negotiation. Even just adding support on READY would provide an opportunity for the server to indicate warnings to clients about protocol initialization issues, like using a deprecated authenticator.
