v135 · miscellaneous

Fenced frames - Automatic beacon cross-origin data support

Fenced frames or URN iframes, if loaded through an API like Protected Audience or Shared Storage, can send out reporting beacons automatically if some event occurs (currently only top-level navigation beacons are supported). We previously tweaked this feature to allow cross-origin documents loaded in the root fenced frame's tree to send automatic beacons if

concepts

  1. Beacon Cross-origin

    The raw beacon payload — auto-emitted on top-nav, now carrying cross-origin data the embedder controls.

  2. UPI-style three-actor data flow

    The Privacy Sandbox scenario: creative renders inside a fenced frame, click-through fires the auto-beacon to a different reporting origin without breaking the privacy fence.

  3. Automatic beacon builder

    Pick event type, destinations, the once flag, and the cross-origin data payload. Watch the resulting setReportEventDataForAutomaticBeacons() call and the generated POST body update live.

  4. Beacon Policy Explorer

    Configure the three-party setup (publisher, ad-tech, reporting endpoint) and see which cross-origin data combinations Chrome 135 policy permits. Toggle crossOriginExposed and destination type against the full policy matrix, then simulate a beacon dispatch.

why it shipped

Fenced frames or URN iframes, if loaded through an API like Protected Audience or Shared Storage, can send out reporting beacons automatically if some event occurs (currently only top-level navigation beacons are supported). We previously tweaked this feature to allow cross-origin documents loaded in the root fenced frame's tree to send automatic beacons if opted in, but still kept the restriction that only frames that are same-origin to the origin loaded by the API could set the data that would be sent as part of the beacon.

references