It is not clear what you are doing.
Normaly does Login page authenticate users to access a resource in that servers Realm.
Redirecting from foreign servers does not make sense in that access control screnario.
If you redirect to logon page then you start accessing that logon page and get authenticated for that page and not for referring server. Beside that even when you jump back to the server are your logon credentials useless. You cannot check for user name or names.nsf person document. You cannot even check that user has successfully authenticated. The authentication is tracked by browser Cookie and that cookie is not visible on another server.
Ther are complicated scenarios to combine two or more server to use same authentication base. It works only betwen two Domino servers or Domino and WebSphere.