Pass a string naming a directory holding multiple
CA certificates to verify the peer with. If libcurl is built against OpenSSL,
the certificate directory must be prepared using the openssl c_rehash utility.
This makes sense only when used in combination with the
#CURLOPT_SSL_VERIFYPEER option.
The #CURLOPT_CAPATH function apparently does not work in Windows due
to some limitation in openssl.