Koichi Kato focused on security hardening within the Zimbra/zm-mailbox repository, addressing credential governance by restricting password changes to administrators. He implemented explicit token-based privilege checks in Java, ensuring only users with admin authentication could modify other accounts’ credentials. This backend development effort closed a vulnerability where non-admin users might alter passwords, directly reducing the risk of unauthorized access. By enhancing auditability and enforcing strict authentication protocols, Koichi’s work improved both security posture and traceability. The depth of the solution lay in integrating privilege validation into existing authentication flows, demonstrating a strong grasp of backend security and authentication best practices.