CURLOPT_SSLENGINE(3)

okay bestie, welcome to CURLOPT_SSLENGINE(3) from the libcurl manual — yes, the Library Functions Manual corner of the group chat. This page is all about setting your SSL engine or provider, and it’s honestly less scary than it sounds. 🫶✨

✨ NAME ✨

CURLOPT_SSLENGINE — Set SSL engine or provider

🌸 SYNOPSIS 🌸

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSLENGINE, char *id);

💅 DESCRIPTION 💅

Okay so you pass a pointer to a null-terminated string as the parameter. That string is used as the identifier for the engine or provider you want to use for your private key. OpenSSL 1 had engines, OpenSSL 3 has providers. No cap. 🔥

The application does not have to keep the string around after setting this option. So you can let it go, bestie — libcurl is not asking you to hold onto it. 💜

When asking libcurl to use a provider, the application can also optionally provide a property — a set of name value pairs. Such a property can be specified separated from the name with a colon (:). iykyk. 🦋

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

🎀 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: OpenSSL.

🌈 EXAMPLE 🌈

Here’s the example — yes, it’s serving main character energy:

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_SSLENGINE, "dynamic");
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

👑 AVAILABILITY 👑

Added in curl 7.9.3.

💖 RETURN VALUE 💖

• CURLE_OK — Engine found.
• CURLE_SSL_ENGINE_NOTFOUND — Engine not found, or OpenSSL was not built with engine support.
• CURLE_SSL_ENGINE_INITFAILED — Engine found but initialization failed.
• CURLE_NOT_BUILT_IN — Option not built in, OpenSSL is not the SSL backend.
• CURLE_UNKNOWN_OPTION — Option not recognized.
• CURLE_OUT_OF_MEMORY — Insufficient heap space.

⭐ SEE ALSO ⭐

• CURLINFO_SSL_ENGINES(3)
• CURLOPT_SSLENGINE_DEFAULT(3)
• CURLOPT_SSLKEY(3)

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mwah 💋 and that’s the whole vibe. This page is from the libcurl manual, source/version libcurl, dated 2026-10-12. Bye bestie, slay your TLS setup! 🧚‍♀️💜