How do sites get my photo from the social network?

Question

JavaScript

About two years ago I met many sites that imitate a message from VKontakte, and my photo was inserted there (accordingly, I was authorized at this VKontakte). So now I asked myself this question, how is this possible? Is it a frame or a cross-domain request or some kind of api, how did they do it technically?

Answer 1

OAuth, social media APIs

Answer 2

Here is another article for general development.

Answer 3

It seems to be like embedding a widget on a page and using it to identify it.