IsSane in objects.go enforces that the SimpleHTTPS token is base64, but the token generated by SimpleHTTPSChallenge in challenges.go is random from util.go, and quite probably nonsense in base64. Looks like all we really want to know is whether it’s bytes characters long and ASCII?

I've started a test case to call validate inside the VA to exercise the sanity check (which wasn't covered before) which exposed the issue. The test is disabled for now, as it will break the build.