DDSSEC12 — serialized_local_participant_data passed to Auth plugin

When the middleware calls Auth plugin operations begin_handshake_request and begin_handshake_reply, it must provide serialized_local_participant_data as an OctetSeq according to serialization rules described in 8.3.2.11.4-5. However, these sections do not specify that padding bytes in the serialized data should be initialized to 0. This is desirable so that the OctetSeq can be hashed with consistent results.

Alternatively, revisit the choice to use OctetSeq here in the plugin API. It seems like it would be fine to pass the structure ParticipantBuiltInTopicDataSecure directly to the plugin, as is already done with Access Control.