public void setAuthenticationCache(Cache<Object, AuthenticationInfo> authenticationCache) {
        this.authenticationCache = authenticationCache;
    }
Sets an explicit {@link Cache} instance to use for authentication caching.  If not set and authentication
caching is {@link #isAuthenticationCachingEnabled() enabled}, any available
{@link #getCacheManager() cacheManager} will be used to acquire the cache instance if available.
<p/>
<b>WARNING:</b> Only set this property if safe caching conditions apply, as documented at the top
of this page in the class-level JavaDoc.

@param authenticationCache an explicit {@link Cache} instance to use for authentication caching or
                           {@code null} if the cache should possibly be obtained another way.
@see #isAuthenticationCachingEnabled()
@since 1.2
core/src/main/java/org/apache/shiro/realm/AuthenticatingRealm.java