CURLOPT_SSLKEYTYPE man page
CURLOPT_SSLKEYTYPE — set type of the private key file
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSLKEYTYPE, char *type);
Pass a pointer to a zero terminated string as parameter. The string should be the format of your private key. Supported formats are "PEM", "DER" and "ENG".
The format "ENG" enables you to load the private key from a crypto engine. In this case CURLOPT_SSLKEY(3) is used as an identifier passed to the engine. You have to set the crypto engine with CURLOPT_SSLENGINE(3). "DER" format key file currently does not work because of a bug in OpenSSL.
The application does not have to keep the string around after setting this option.
All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
If built TLS enabled.
Returns CURLE_OK if TLS is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.
curl_easy_setopt(3), CURLOPT_PROXY_SSLKEY(3), CURLOPT_PROXY_SSLKEYTYPE(3), CURLOPT_SSLKEY(3).