Can I consider as confirmed email received via oauth of popular social networks?

Question

Facebook

User A registers on my site via email [email protected] and a password. Next, user B enters my site - he earns to enter through VKontakte, I get the email of user B from VK - [email protected] on the server, I see that I already have a user with such mail. What is the right thing to do: log in user B to user A's account? those. Interested in whether social networks: vk, facebook, ok are guaranteed in practice that the email that they gave me was confirmed by the user? How do you deal with such cases?

Answer 1

Say that you already have such an account and enter the code from the letter to bind.