An extension to the Storage Access API that allows a top-level site to request access to unpartitioned ("first-party") cookies on behalf of embedded sites. Browsers will have discretion to grant or deny access, with mechanisms like Related Website Set membership as a potential signal. This allows for use of the Storage Access API by top-level sites.
Multiple browsers supporting the Storage Access API have implemented an internal API similar to requestStorageAccessFor, indicating it is useful for websites that depend on authenticated/personalized content served from cross-site origins. We intend it to aid in unblocking certain cross-site, same-First-Party Set use cases previously addressed by the now-archived SameParty cookie attribute.
Explainers: https://github.com/privacycg/requestStorageAccessFor