Keycloak: concurrent failed logins can lock accounts on MySQL clusters

A flaw was found in the login-failure storage component of Keycloak, the identity and access management solution. This issue specifically affects deployments using MySQL or MariaDB databases in a multi-node configuration. When multiple failed login attempts occur simultaneously for the same account, a synchronization error can cause the system to enter a repetitive loop that locks the user's record in the database. This results in legitimate login attempts for that user being blocked and failing with an error. Furthermore, because some failures are not correctly recorded during this loop, the system's brute-force protection may not accurately count all failed attempts.