Oh, I didn't realize a subdomain was not considered 3rd party. So soon we'll see adnetwork.mydomain.com and www.mydomain.com.
I think we should just make cookies only work when the domain matches exactly.
I think we should just make cookies only work when the domain matches exactly.
Advertisers can't trust content people to forward requests because it would be too easy to fake them.
However a server like nginx can be set up to proxy requests matching a specific url pattern to another server. This would be a bit more work than adding a DNS entry and referencing that though.
That's why the ad industry used third-party domains in the first place, BTW - it's a zero-setup solution. Subdomains are minimal-setup; subdirectories are a huge hassle.
Another reason is ad provider doesn't have to trust first party, if ads are served from their server.
I'm not sure which reason is more important.
Easier than changing a cname.