How to determine a user profile from social. networks?

Question

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Hello, please help me with the following question.
Now, on many callback sites, there is a function for defining a profile in a social network, for example, VKontakte. When a person simply enters the site, the manager already sees his profile on the network.
Can you suggest how this is done?
I searched for information, but something was unsuccessful, I found that the widget is hidden, but it seems to me that this information is not relevant.

Answer 1

at the moment, VK does not provide such functionality, all such services can only work through some kind of internal data drain. For example, I.metrics VK merges data, in other cases I have not met a service where it would somehow work sanely .

Answer 2

Previously, clickjacking was used, now, probably, there are also some hacks. In any case, this is done in violation of all VK rules, a frankly gray (if not black) scheme. Use VK retargeting and everything will be ok.