A Vault administrator have associated a logon account to one of their Unix root accounts...

According to the web search results, when a Vault administrator has associated a logon account to one of their Unix root accounts in the vault, the CPM will log in first with the logon account, then run the SU command to log in as root using the password in the Vault1. This is a common use case for using a logon account, as the best practice for Unix systems is to disallow the root user from logging in using SSH, which is what the CPM uses to sign in to a system to manage the password2. The logon account can be defined on the target account level or on the platform level, making it available to all accounts associated with the platform2. The CPM can also use the logon account to initiate PSM sessions to the target machine3.