Consider applying filtering before prioritization during attribution step

[johnivdel]

Related to #491

The browser first finds the highest priority impression, then checks if it matches filters before attributing it. This means, if there are two impression with the same priority, where the first matches and the latter does not, the adtech will not receive a report.

[apasel422]

Would a source whose destination and reporting origin match those of the trigger but whose filter data does not match the trigger's filters be deleted?

In other words, would the criteria for matchingSources be changed to include the filter matching under this proposal? Or just the subsequent steps for finding the highest-priority element of matchingSources whose filter data matches?

[alois-bissuel]

Digging up this old issue, we would be quite interested to have the filtering step done before the attribution.
I am not sure to fully understand @apasel422 's two proposals though.

[vikassahu29]

We have recently proposed a new feature where developers can set scopes on sources and triggers to perform pre-attribution filtering. 

https://github.com/WICG/attribution-reporting-api/blob/main/attribution_scopes.md

Please let us know if this meets your needs and any other feedback you might have!