Per-device USDID identity. Generated once and persisted in MobileDevice.
Sent to the server via IGUSDIDRegistrationMutation (graphql_www).
The mutation establishes the binding (usdid uuid, device public key, family device id)
server-side. Subsequent traffic identifies the device by the USDID and proves
possession with signatures over the embedded EC P-256 private key.
Per-device USDID identity. Generated once and persisted in
MobileDevice.Sent to the server via
IGUSDIDRegistrationMutation(graphql_www). The mutation establishes the binding(usdid uuid, device public key, family device id)server-side. Subsequent traffic identifies the device by the USDID and proves possession with signatures over the embedded EC P-256 private key.