How to link different authorization methods in one account?

Question

ASP.NET

Good afternoon!
I am developing an application (website) on which I want to provide access via login / password and through various social networks. The question is how to make the system consider the inputs of the same person through different authentication systems as a single account?
Those. a person entered through the form - was displayed on the site as User1. I went through VK - it was displayed on the site as the same User1.
As far as I know, in the user table, each type of login corresponds to a separate line.

Answer 1

The easiest way is to identify by email.
However, it is less secure - if someone steals a user's account on some social network, then he will be able to impersonate him.
Therefore, it is worth creating an internal user account and linking others to it.

Answer 2

Well, on the Users table with the "login, password" fields, the light did not converge like a wedge. Add a table like UsersInSocial where you store the UserId bindings and account data of the social network associated with this user. When authenticating using the second table, specify who it is.