How to get the user id or username of the person who shared the link?

Question

Facebook

The user "share" a link to the site through a button on the page, is it possible to get information about his account (he is authorized at the same time) - id or username. First of all, we are interested in a similar opportunity for services: vk, fb, tw.

Answer 1

When a post is shared inside VKontakte, in the iFrame application, via wall.post(), the post id on its wall is returned, and you already know the post id. I did this mechanic: the user, post id, and through the def. the time is checked to make sure it is still hanging on the wall and contains the right text - for the user to receive a reward.
If a person shares a link on an external site through the “Like” widget , only the number of likes of this page is returned, the user’s identity / id is not disclosed.

Answer 2

No
such possibility - vulnerability