Since the target of any links to the CUG Realm are not visible to the anonymous user, the linkchecker will remove such links.
To avoid this, it is advisable to create non-protected redirect pages that point to pages within the CUG Realm. The navigation entries are then rendered without causing the linkchecker any problems. Only when actually accessing the redirect page will the user be redirected inside the CUG Realm - after successfully providing their login credentials.