CURLOPT_SSLKEY - Man Page

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSLKEY, char *keyfile);

Pass a pointer to a null-terminated string as parameter. The string should be the filename of your private key. The default format is "PEM" and can be changed with CURLOPT_SSLKEYTYPE(3).

(Windows, iOS and macOS) This option is ignored by Secure Transport and Schannel SSL backends because they expect the private key to be already present in the key-chain or PKCS#12 file containing the certificate.

The application does not have to keep the string around after setting this option.

Using this option multiple times makes the last set string override the previous ones. Set it to NULL to disable its use again.

NULL

This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

This option works only with the following TLS backends: OpenSSL, Schannel, mbedTLS and wolfSSL

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_SSLCERT, "client.pem");
    curl_easy_setopt(curl, CURLOPT_SSLKEY, "key.pem");
    curl_easy_setopt(curl, CURLOPT_KEYPASSWD, "s3cret");
    res = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

Added in curl 7.9.3

Returns CURLE_OK if TLS is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.

CURLOPT_SSLCERT(3), CURLOPT_SSLKEYTYPE(3), CURLOPT_SSLKEY_BLOB(3)

curl_easy_setopt(3), CURLOPT_KEYPASSWD(3), CURLOPT_PROXY_KEYPASSWD(3), CURLOPT_PROXY_SSLKEY(3), CURLOPT_PROXY_SSLKEY_BLOB(3), CURLOPT_SSLCERT(3), CURLOPT_SSLCERT_BLOB(3), CURLOPT_SSLCERTTYPE(3), CURLOPT_SSLENGINE(3), CURLOPT_SSLKEY_BLOB(3), CURLOPT_SSLKEYTYPE(3), libcurl-symbols(3).