A proprietary protocol for iBoot devices is used for control and keepalive commands. The function compares the username and password; it also contains the configuration data for the user specified. If the user does not exist, then it sends a value for username and password, which allows successful authentication for a connection.
https://www.cisa.gov/news-events/ics-advisories/icsa-22-263-03
https://dataprobe.com/support/iboot-pdu/local_upgrade_pdu_procedure.pdf