How to store an authorization session?

Question

Web development

I work with the VKontakte API and a question has arisen: after the user is authorized through VK, I throw a unique key in cookies, while saving the first name, last name, id, photo in the database. After the user has logged out, I delete the cookie, but how do I know when I log in to the site again that this particular user was using it?
Please explain the principle of storing data and re-authorization on the site through the API.
What do I need to store in the database when re-authorization?

Answer 1

No, you specifically deleted the cookie when he logged out.
Try to understand for yourself what you are doing and why.
Then try to describe what you want to change.