On what principle is VKontakte authorization built?

Question

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Good day, colleagues! I am writing a system that implies the presence of user authorization.
As an example, I consider the functionality of a number of social platforms. One of them is VK.
Who knows on what basis authorization is built on this service? Why is it regenerated when I clear the whole date? How and where are user sessions stored? What technologies are used?
Thank you in advance!

Answer 1

https://vk.com/dev/access_token

Answer 2

This is banal OAuth 2