httputil: only send client authorization over HTTPS

Might just be a hypothetical concern, but better for this to fail closed
(not send credentials when needed) than to fail open (send credentials
insecurely).

Change-Id: I8542e8c0b533a3c5f53a5f03f4e3b639b6b55f71
Reviewed-on: https://go-review.googlesource.com/69290
Reviewed-by: Tuo Shan <shantuo@google.com>
2 files changed