Where is the CSRF token stored on the server?

Question

Yii

Tell me, when a csrf token arrives from the client to the server, then where does the server take the csrf token to compare with the one that arrived from the client? Is it stored in the session?

In general, the problem is the following. There is a site on yii2. It has the following registration logic: the user registers, then confirms the registration by email, and then logs in through the form.
And if you register (we DO NOT close this page after registration), then confirm the registration using the link in another browser, then return to the browser in which you registered and try to log in, then an error 400 comes in response - it was not possible to check the data. I understand that most likely because of csrf. But I don't understand the logic