how to clear cache objects for certain user

[Karsten Priegnitz]

Hello,

I want to clear the cached data for a certain user. All I have in my 
hand is the username, which is not the name of the user which is logged 
in. No Principle objects, Realms and so on. What I tried is this:

        for (Realm realm : realms) {
            if (!(realm instanceof AuthorizingRealm)) {
                continue;
            }

            final org.apache.shiro.cache.Cache<Object, 
AuthorizationInfo> zcache = ((AuthorizingRealm) 
realm).getAuthorizationCache();

            LOG.debug("cached credentials found for {}", realm.getName());

            for (final Object key : zcache.keys()) { // zcache.keys() 
is always empty
                final PrincipalCollection principals = 
(PrincipalCollection) key;

                // what to do now?
                // I want to delete everything for String username
            }
        }

But I even don't get to the "what to do now" line, because zcache.keys() 
is always empty.

I'm using shiro 1.2.3 and ehcache with standard config.

Best,
Karsten