@mivi.ftrc: Thanks for sharing! That may be a bug report for Apple as that contradicts their statement on ephemeral sessions:
This setting asks the browser to avoid using any existing browsing data, like cookies, during the authentication process. It also asks that the browser avoid retaining any data collected during the authentication attempt beyond the lifetime of the attempt, or sharing it with any other session.
(emphasis added, https://developer.apple.com/documentation/authenticationservices/authenticating_a_user_through_a_web_service?language=objc, heading: “Optionally Request Ephemeral Browsing”)
It would be helpful to just update the clearSession to support this.
Can you elaborate on this request? Are you asking for a documentation update, or to have clearSession run with prefersEphemeralSession?