How to identify the same user from different browsers?

Question

Information Security

Hello!
In one of the projects, it is necessary to define the user cross-browser.
I used crosscookie, evercookie, flashcookie - nothing works cross-browser :(
Thank you so much for the answers!

Answer 1

Let him sign in

Answer 2

And will not work - flush, this is the maximum

Answer 3

Try to save ip. And compare them at regular intervals. If there is a match, then to the user with the already existing ip on the site who logged in later, issue a message: "User with this ip is already on the site. Immediately close the browser tab and turn off the computer. And sockets"
=)