Why does vk use a login redirect?

Question

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The initial request is made to login.vk.com, then, as I understand it, it is redirected to vk.com. So why is this being done?

Answer 1

Probably another layer of security. there they put cookies purely on the login.vk subdomain for a year + HttpOnly.
on the main domain, cookies are set on all subdomains (and without HttpOnly), which is less secure in the case of xss.
that is, reliable cookies are stored on this subdomain, which cannot be stolen through xss. and these cookies do not fly with all requests, and it will be more difficult to hijack someone else's session.