when I share some content in FB via the "Social Sharing" option, a user who is not registered gets the information, that he can only view this content if he is registered n this site and that he has to register ....

What I am missing here is a link to the registration page or to the homepage (that in our case contains the LogIN Box with all the information about how to register ...

How could such a link be implemented? Would be very helpful. or is there another / better solution already in available?