I have a webpage (in Drupal 6) which contains a Facebook like button, a comment box like. The Facebook receives through open graph tags the information which has to be shared. This site is not accessible for anonymous users, only for registered users.
When an anonymous user tries to open the site, he's redirected to the log in page. Here comes the problem: when Facebook scans the page to receive the information which should be shared, the site handles as anonymous user and redirects to the log in page. So the Facebook receives the log in page's information (image, description). Can I decide/verify somehow when the Facebook is trying to scan my site to avoid to redirect it to the log in page (somehow without Facebook API)?