Handle PSS padding in cryptoapicert

Handle PSS padding in cryptoapicert

For PSS padding, CNG requires the digest to be signed
and the digest algorithm in use, which are not accessible
via the rsa_sign and rsa_priv_enc callbacks of OpenSSL.
This patch uses the EVP_KEY interface to hook to
evp_pkey_sign callback if OpenSSL version is > 1.1.0.

To test this code path, both the server and client should
be built with OpenSSL 1.1.1 and use TLS version >= 1.2

Tested on Windows 7 client against a Linux server.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1548863600-491-1-git-send-email-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg18188.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>