public String getValue() {
        String value = null;

        Subject subject = SecurityUtils.getSubject();
        Session session = subject.getSession(false);
        if (session != null) {
            value = (String) session.getAttribute(VALUE_KEY);
            if (LOGGER.isDebugEnabled()) {
                LOGGER.debug("retrieving session key [" + VALUE_KEY + "] with value ["
                        + value + "] on session with id [" + session.getId() + "]");
            }
        }

        return value;
    }
Key used to store the value in the user's session.
samples/spring-mvc/src/main/java/org/apache/shiro/samples/spring/DefaultSampleManager.java