curl / libcurl / API / curl_easy_setopt / CURLOPT_ISSUERCERT

CURLOPT_ISSUERCERT explained

Name

CURLOPT_ISSUERCERT - issuer SSL certificate filename

Synopsis

#include <curl/curl.h>
 
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ISSUERCERT, char *file);

Description

Pass a char pointer to a null-terminated string naming a file holding a CA certificate in PEM format. If the option is set, an additional check against the peer certificate is performed to verify the issuer is indeed the one associated with the certificate provided by the option. This additional check is useful in multi-level PKI where one needs to enforce that the peer certificate is from a specific branch of the tree.

This option makes sense only when used in combination with the CURLOPT_SSL_VERIFYPEER option. Otherwise, the result of the check is not considered as failure.

A specific error code (CURLE_SSL_ISSUER_ERROR) is defined with the option, which is returned if the setup of the SSL/TLS session has failed due to a mismatch with the issuer of peer certificate (CURLOPT_SSL_VERIFYPEER has to be set too for the check to fail). (Added in 7.19.0)

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

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

Default

NULL

Protocols

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

This option works only with the following TLS backends: GnuTLS and OpenSSL

Example

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_ISSUERCERT, "/etc/certs/cacert.pem");
    res = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

Availability

Added in curl 7.19.0

Return value

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