Inject Spring Security's SessionAuthenticationStrategy (ChangeSessionIdAuthenticationStrategy) into AuthSessionController and invoke onAuthentication at the credential boundary. The strategy calls HttpServletRequest.changeSessionId() to invalidate any pre-auth session ID an attacker may have planted and mint a fresh ID before the SecurityContext is attached. Addresses PR #612 / Nora B1. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>