Advertiser's control over Interest Group merging

[jonasz]

Hi all,

During last two public calls there was discussion about the differences in the privacy model between Ad Selection API and Protected Audience API. More specifically, as mentioned in API difference highlihgts, in Ad Selection API Interest Groups are

Partitioned by domain on disk and in transit, merged in trusted/transient/opaque env.

One aspect discussed during the calls was what these differences mean from the perspective of the advertiser. For better visibility and tracking, I'd like to file this issue and describe RTB House's feature request for better advertiser's control over Interest Group merging.

We see value in the advertiser being able to specify whether their interest group should be processed in isolation, or if it can be merged and processed with other IGs (created when user visited different toplevel domains) when generateBid is run. We propose that this behavior be controlled by a dedicated parameter during a call to joinAdInterestGroup. It'd also be valuable if the value of this parameter is easily inspectable in the created IGs (for example through DevTools). The value this brings is that advertisers can inspect their technical integration with AdTechs, and make sure the browser will technicaly enforce that their IGs are isolated during generateBid.

Some more detailed discussion on this was held on 2024-03-21 (notes), and 2024-04-04 (notes).

Best regards,
Jonasz