Specify directory holding ca certificates
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CAPATH, char *capath);
Pass a char * to a zero terminated 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(3) option.
The CURLOPT_CAPATH(3) function apparently does not work in Windows due to some limitation in openssl.
All TLS based protocols: HTTPS, FTPS, IMAPS, POP3, SMTPS etc.
This option is OpenSSL-specific and does nothing if libcurl is built to use GnuTLS. NSS-powered libcurl provides the option only for backward compatibility.
Returns CURLE_OK if TLS enabled, and CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.