VK API and FB API. How to check the repost on the wall of a specific user?

Question

Facebook

Hey! I want to make such a scenario: a user on my site pokes a repost of the landing page on his wall. The service looks at him on the wall after a while, checks. If the repost is in place then true.
I looked at the API and did not find how I can catch the id of the reposter on my site, so that later I can look at his wall.
Tell me how best to implement this scheme in fb and vk?
Perhaps I found a solution for the contact:

VK.init({
apiId: vkAppID
});
VK.Widgets.Like("vk_like", {type: "button"});
VK.Observer.subscribe("widgets.like.liked", function f(){
alert ("Thank you for your like.");
});
VK.Observer.subscribe("widgets.like.shared", function f(){
alert("Thank you for your shared.");
});

But it is not clear how to get the profile ID.

Answer 1

In facebook, you can get the entire feed using
Plus after you made a post (for example, using js FB.ui) as a result, you will get a unique post id and you can check if it exists by calling
But for this you need to request the rights to user_posts
VK also returns the id of the post, but unfortunately I don't know how to use it.