--pinnedpubkey for unsupported TLS backends

[bagder]

I did this

Used --pinnedpubkey with curl built with a TLS backend without support for it. But it doesn't complain on bad keys.

I expected the following

It needs to warn or error out when the option is used without support in libcurl so that the problem is not silently ignored.

Ray's initial patch for this

Also see this additional gskit patch

I'm assigning you Jay since you were on track on this before. Let me know if you're not fine with that, then I can take over instead.

cc: @moparisthebest

[moparisthebest]

I'll paste and update this from my mailing list email as well:

these backends
implementations are unsupported:

axtls.c - looks unlikely to ever be supported after glance at docs
darwinssl.c - stalled
schannel.c - Ray said someone was working on this? who/where?

and these have partial support:

cyassl.c only support #ifdef KEEP_PEER_CERT
gskit.c only support pem/der, needs curlssl_sha256sum defined for hash
support

of course that leaves these with full support:

gtls.c
mbedtls.c
nss.c
openssl.c
polarssl.c

[bagder]

Committed a fix for this in commit 283babf. Please try it out and see if there's anything missing now.