Specific access through redirection from other website/domain

We would like a new access right which is dependent on where the user was redirected from previously. For example:

We have a page where users log in and on that page we have a link to our xWiki. The users who log in should have read-only access (in our case, could be a new access right where admins can change access level) to the xWiki, but if users aren't logged in on the page and try to access the xWiki, they will only get to the login page of the xWiki.

So I thought that admins could set a domain or webpage as an "accepted visitation through"-variable and it only allows access to the xWiki (with also set restricted rights) through that webpage or domain.