in pan-domain-auth-play/src/main/scala/com/gu/pandomainauth/action/Actions.scala [212:219]
def flushCookie(result: Result): Result = {
val clearCookie = DiscardingCookie(
name = settings.cookieSettings.cookieName,
domain = Some(domain),
secure = true
)
result.discardingCookies(clearCookie)
}