/**
     * Gets the current preauth hash for a session.
     *
     * @param sessionId the session identifier
     * @return the current hash, or null if no context exists
     */
    public byte[] getCurrentPreauthHash(String sessionId) {
        PreauthIntegrityContext context = sessionContexts.get(sessionId);
        return context != null ? context.getCurrentHash() : null;
    }

    /**

        assertNotNull(preauthService.getCurrentPreauthHash(sessionId1));
        assertNotNull(preauthService.getCurrentPreauthHash(sessionId2));

        preauthService.cleanup();

        assertNull(preauthService.getCurrentPreauthHash(sessionId1));
        assertNull(preauthService.getCurrentPreauthHash(sessionId2));
    }