CURLOPT_ISSUERCERT(3)

🌸 NAME 🌸

CURLOPT_ISSUERCERT — issuer SSL certificate filename 💖

okay so real talk, bestie: this page is from the Library Functions Manual, and it's all about CURLOPT_ISSUERCERT(3) — the option where libcurl checks the peer certificate's issuer against a CA certificate file you hand it. 👑

✨ SYNOPSIS ✨

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ISSUERCERT, char *file);

💅 DESCRIPTION 💅

Okay so you 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(3) 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(3) has to be set too for the check to fail). 😭💀
• 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 result;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_ISSUERCERT, "/etc/certs/cacert.pem");
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

🔥 AVAILABILITY 🔥

Added in curl 7.19.0 ✨

👑 RETURN VALUE 👑

curl_easy_setopt(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 💀

• CURLOPT_CRLFILE(3)
• CURLOPT_SSL_VERIFYHOST(3)
• CURLOPT_SSL_VERIFYPEER(3)

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that's the whole page, bestie — libcurl sign-off with date 2026-10-12, page CURLOPT_ISSUERCERT(3). mwah 💋🫶