private String getSharedGroupsForUserKey(final String userName) {
        return USER_SHARED_GROUPS_KEY + userName;
    }
Returns a custom {@link Map} that updates the database whenever
a property value is added, changed, or deleted.

@param group The target group
@return The properties for the given group
xmppserver/src/main/java/org/jivesoftware/openfire/group/AbstractGroupProvider.java