easy:SetOpt_SSLKeyType(type)
The format "ENG" enables you to load the private key from a crypto engine. In
this case #CURLOPT_SSLKEY
is used as an identifier passed to the
engine. You have to get the crypto engine with #CURLOPT_SSLENGINE
.
"DER" format key file currently does not work because of a bug in OpenSSL.