The requestStorageAccessFor (rSAFor) API is 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 Sets (RWS) membership as a potential signal. This allows for use of the Storage Access API by top-level sites. Following Chrome's announcement that the current approach to third-party cookies will be maintained, we are now planning to deprecate and remove rSAFor, as it is only usable in Chrome to request storage access between RWS sites. Related Website Sets will also be deprecated via a separate intent.
Chrome has announced that the current approach to third-party cookies will be maintained. rSAFor currently has usage on about 0.95% of page loads, but any website relying on successful invocation of rSAFor (i.e. the API returns a promise that resolves) must also have registered a set on the RWS GitHub repository. Any invocations of rSAFor outside of an RWS currently returns a promise that is rejected. Our metrics suggest that almost all of the usage of rSAFor is from websites that have registered sets. We will continue to monitor usage and aim to drive it down prior to removal by proactively informing set owners of the deprecation timelines and request them to turn down usage. Additionally, other browser engines have not signaled interest in implementing the API, obviating any interoperability concerns.