CURLINFO_CERTINFO(3)

NAME
CURLINFO_CERTINFO - get the TLS certificate chain

SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_CERTINFO,
                           struct curl_certinfo **chainp);

DESCRIPTION
Pass a pointer to a struct curl_certinfo * and it is set to point to a struct that holds info about the server's certificate chain, assuming you had CURLOPT_CERTINFO(3) enabled when the request was made.
struct curl_certinfo {
  int num_of_certs;
  struct curl_slist **certinfo;
};
The certinfo struct member is an array of linked lists of certificate information. The num_of_certs struct member is the number of certificates which is the number of elements in the array. Each certificate's list has items with textual information in the format "name:content" such as "Subject:Foo", "Issuer:Bar", etc. The items in each list varies depending on the SSL backend and the certificate.

PROTOCOLS
This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc. This option works only with the following TLS backends: GnuTLS, OpenSSL, Schannel, Secure Transport and rustls

EXAMPLE
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL, "https://www.example.com/");
    /* connect to any HTTPS site, trusted or not */
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
    curl_easy_setopt(curl, CURLOPT_CERTINFO, 1L);
    res = curl_easy_perform(curl);
    if(!res) {
      int i;
      struct curl_certinfo *ci;
      res = curl_easy_getinfo(curl, CURLINFO_CERTINFO, &ci);
      if(!res) {
        printf("%d certs!\n", ci->num_of_certs);
        for(i = 0; i < ci->num_of_certs; i++) {
          struct curl_slist *slist;
          for(slist = ci->certinfo[i]; slist; slist = slist->next)
            printf("%s\n", slist->data);
        }
      }
    }
    curl_easy_cleanup(curl);
  }
}
See also the certinfo.c example.

HISTORY
GnuTLS support added in 7.42.0. Schannel support added in 7.50.0. Secure Transport support added in 7.79.0. mbedTLS support added in 8.9.0.

AVAILABILITY
Added in curl 7.19.1

RETURN VALUE
curl_easy_getinfo(3) returns a CURLcode indicating success or error. CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3).

SEE ALSO
CURLINFO_CAPATH(3), curl_easy_getinfo(3), curl_easy_setopt(3)