CURLOPT\_SSLENGINE(3) Library Functions Manual CURLOPT\_SSLENGINE(3)

# [NAME](#NAME)

CURLOPT\_SSLENGINE - Set SSL engine or provider

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSLENGINE, char *id);
```

# [DESCRIPTION](#DESCRIPTION)

Pass a pointer to a null-terminated string as parameter. It 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.

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

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 (*:*).

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

# [DEFAULT](#DEFAULT)

NULL

# [PROTOCOLS](#PROTOCOLS)

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

This option works only with the following TLS backends: OpenSSL

# [EXAMPLE](#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_SSLENGINE, "dynamic");


    result = curl_easy_perform(curl);


    curl_easy_cleanup(curl);


  }
}
```

# [AVAILABILITY](#AVAILABILITY)

Added in curl 7.9.3

# [RETURN VALUE](#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](#SEE_ALSO)

[**CURLINFO\_SSL\_ENGINES**(3)](/man/os/curl/CURLINFO_SSL_ENGINES.3), [**CURLOPT\_SSLENGINE\_DEFAULT**(3)](/man/os/curl/CURLOPT_SSLENGINE_DEFAULT.3), [**CURLOPT\_SSLKEY**(3)](/man/os/curl/CURLOPT_SSLKEY.3)

2026-10-19 libcurl

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Document: CURLOPT_SSLENGINE(3) from curl 8.23.0-r1 (Chainguard OS)
Source: https://github.com/curl/curl.git