How to identify a user using third party cookies

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1

Hey guys,

I have the following problem which I am not able to solve easily:

  1. I have a siteA which sets a cookie for siteA’s domain (lets call it domainA). When the user comes back to siteA, I can log her in via the cookie.

  2. Now the client wants, that even if the user removed all cookies for domainA, I can identify her when she comes back to siteA.

I have read up on third party cookies, but I don’t know what the flow would be to do this.
Like I set a cookie for domainB on siteA, include a hidden iframe pointing to domainB, and by that be able to also read cookies from siteB on siteA?

Does anybody have any experience with this?

Thank you for your time.

2

Cannot. If the user removes all cookies for DomainA, ALL COOKIES ARE REMOVED. NO EXCEPTIONS.
Cookies also cannot be read from other domains, DomainA cannot read cookies from DomainB. NO EXCEPTIONS.