Service Worker should correctly set its document first party for cookies URL. It seems to have regressed in https://trac.webkit.org/changeset/230944/webkit.
Created attachment 384607 [details] Patch
Comment on attachment 384607 [details] Patch Clearing flags on attachment: 384607 Committed r252985: <https://trac.webkit.org/changeset/252985>
All reviewed patches have been landed. Closing bug.
<rdar://problem/57559730>