curl / libcurl / API / curl_easy_getinfo / CURLINFO_CERTINFO

CURLINFO_CERTINFO explained

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 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 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);
  }
}

History

GnuTLS support added in 7.42.0. Schannel support added in 7.50.0. mbedTLS support added in 8.9.0.

Availability

Added in curl 7.19.1

Return value

curl_easy_getinfo returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors.