This is useful to CAs, to identify and reach out to problematic clients. Fixes golang/go#24496 Change-Id: I944fc8178c8fa8acaf3854e9c125d3af0364a4fb Reviewed-on: https://go-review.googlesource.com/c/crypto/+/183267 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>