The Storage Access API allows third-party embeds to request access to their first-party cookies when the user interacts with them. It also offers the embedding top frame a new iframe sandbox token allow-storage-access-by-user-activation The API offers two new functions to cross-origin iframes. WebKits implementation of the API only covers cookies for now. It does not affect the partitioning of other storage forms such as IndexedDB or LocalStorage.”]
Source: https://webkit.org/blog/8124/introducing-storage-access-api/