Mention per-frame rSA interaction #7
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Also clarify CORS use-credentials.
johannhof
approved these changes
Jan 10, 2023
| * `SameSite=None` cookies granted via requestStorageAccessForOrigin on subresources should only be attached on CORS-enabled requests. For example, an `<img>` without a [`crossorigin` attribute](https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/crossorigin) would not have `SameSite=None` cookies attached, even with a valid grant. This ensures the server is aware of the caller and can react accordingly. Note that CORS is not possible on navigations; this requirement is not intended to protect `<iframe>` elements, which have other mechanisms for forbidding embedding (e.g., `x-frame-options` or `CSP`). | ||
| * For nested resource loads, [a variant of the site for cookies algorithm](https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-rfc6265bis-10#section-5.2.1) could be used to avoid unrelated iframes from using a grant, potentially with a permission policy opt-out, as suggested in [a recent security analysis](https://github.com/privacycg/storage-access/issues/113). | ||
| * Another alternative would be requiring explicit per-frame opt-in via normal `requestStorageAccess` call; see below. | ||
| * `SameSite=None` cookies granted via `requestStorageAccessForOrigin` on subresources should only be attached on CORS-enabled requests. For example, an `<img>` without a [`crossorigin` attribute](https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/crossorigin) set to `use-credentials` would not have `SameSite=None` cookies attached, even with a valid grant. This ensures the server is aware of the caller and can react accordingly; because the response must have the appropriate header to be read by the embedder, this ensures the embeddee has opted in. Note that CORS is not possible on navigations; this requirement is not intended to protect `<iframe>` elements. |
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I think this was technically mentioned in the issue and document, but it's fine listing it here :)
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Also clarify CORS use-credentials.