Custom Return URLs Upon Success in the same post

Hi,
i’d like to set the Custom Return URLs Upon Success using success attribute to redirect user to the same content he was reading before authentication.

For example:
i am subscribed, but not yet logged in, and i’m reading a post with a restrict content so i can read only the first lines of the article… i log in (with login widget) and i want to see all the content unblocked without returning manually to the same post.