CURLOPT_PROXY_KEYPASSWD - passphrase for the proxy private key
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_KEYPASSWD, char *pwd);
This option is for connecting to an HTTPS proxy, not an HTTPS server.
Pass a pointer to a null-terminated string as parameter. It will
be used as the password required to use the CURLOPT_PROXY_SSLKEY(3)
private key. You never needed a pass phrase to load a certificate but you
need one to load your private key.
The application does not have to keep the string around after
setting this option.
CURL *curl = curl_easy_init();
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
curl_easy_setopt(curl, CURLOPT_PROXY, "https://proxy:443");
curl_easy_setopt(curl, CURLOPT_PROXY_KEYPASSWD, "superman");
ret = curl_easy_perform(curl);
Returns CURLE_OK if TLS enabled, CURLE_UNKNOWN_OPTION if not, or
CURLE_OUT_OF_MEMORY if there was insufficient heap space.