AKS ACI usage (versus ASK CC) in buyer-seller-services

[dankocoj-google]

We are seeking to understand Microsoft's decision to use AKS ACI in adSelection. Did Microsoft consider alternate approaches such as AKS CC, and if so what tradeoffs led to the choice of AKS ACI? During the WICG call on Jan 9, we were told by Slava & Isaac from Microsoft that the decision to use AKS-ACI was due to some security considerations. Can you shed more light on this? Thanks in advance.