Add Clarifying Note About Cross Origin Retrieval Header for Delegatio…

…n File (#1029)

Ran into this while testing, probably should be assumed but wanted to save someone else the trouble.

FLEDGE.md

@@ -292,7 +292,7 @@ If any of these per-owner limits are exceeded, the interest group(s) that would
 
 #### 1.3 Permission Delegation
 
-When a frame navigated to one domain calls joinAdInterestGroup(), leaveAdInterestGroup(), or clearOriginJoinedAdInterestGroups() for an interest group with a different owner, the browser will fetch the URL https://owner.domain/.well-known/interest-group/permissions/?origin=frame.origin, where `owner.domain` is domain that owns the interest group and `frame.origin` is the origin of the frame. The fetch uses the `omit` [credentials mode](https://fetch.spec.whatwg.org/#concept-request-credentials-mode), using the [Network Partition Key](https://fetch.spec.whatwg.org/#network-partition-keys) of the frame that invoked the method. To avoid leaking cross-origin data through the returned Promise unexpectedly, the fetch uses the `cors` [mode](https://fetch.spec.whatwg.org/#concept-request-mode). The fetched response should have a JSON MIME type and be of the format:
+When a frame navigated to one domain calls joinAdInterestGroup(), leaveAdInterestGroup(), or clearOriginJoinedAdInterestGroups() for an interest group with a different owner, the browser will fetch the URL https://owner.domain/.well-known/interest-group/permissions/?origin=frame.origin, where `owner.domain` is domain that owns the interest group and `frame.origin` is the origin of the frame. The fetch uses the `omit` [credentials mode](https://fetch.spec.whatwg.org/#concept-request-credentials-mode), using the [Network Partition Key](https://fetch.spec.whatwg.org/#network-partition-keys) of the frame that invoked the method. To avoid leaking cross-origin data through the returned Promise unexpectedly, the fetch uses the `cors` [mode](https://fetch.spec.whatwg.org/#concept-request-mode). The fetched response should have a JSON MIME type, have a `Access-Control-Allow-Origin` that allows it to load from the calling origin, and be of the format:
 
 ```
 { "joinAdInterestGroup": true/false,