Context

Publishers today can rely on their SSP/Analytics partners to provide detailed reporting on several metrics and analytical tooling outside of the reporting provided by their ad server.
e.g. Prebid supports analytics adapters that receive events notifying them of bid initiation, bidder adapter bids, timeouts, etc. allowing for data analysis in the analytics vendors interface.
The current PA-API implementation doesn't allow for more than one entity (the top-level seller) to view and thus report on all the component and top-level auctions.

Proposal

The PA-API adds an analyticsURL key to the auction config that takes a URL to a hosted javascript file as a value.
The hosted file can contain a function that is called when each participating component auction and the top-level auction's reportResult() function is called.

This function's input schema and restrictions can be similar to the existing reportResult().