i really don't get the hoopla advertising folks are making about Mozilla dropping third party cookie support. It's like they completely forgot how they used to do business.
To solve the "No Third Party Cookies" issue, you simply make the third party stuff first party.
That means the content serving site makes a call to your ad serving site for the ad to display, possibly passing additional info like a local user ID. The ad site then does the same sort of lookup it did before and returns the HTML directly to the content site. Which means that the content site gets to expose page metrics to the ad site (which it kinda already does) and the ad site has to have a good
Oh, what's that Ad providers? You're worried about your proprietary information leaking to parties who have a vested interest in exploiting it?