CURLOPT_SSL_CTX_DATA(3)    Library Functions Manual    CURLOPT_SSL_CTX_DATA(3)

NAME
       CURLOPT_SSL_CTX_DATA - pointer passed to SSL context callback

SYNOPSIS
       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_DATA, void *pointer);

DESCRIPTION
       Data pointer to pass to the SSL context callback set by the option
       CURLOPT_SSL_CTX_FUNCTION(3), this is the pointer you get as third
       parameter.

DEFAULT
       NULL

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,
       mbedTLS and wolfSSL

EXAMPLE
       /* OpenSSL specific */

       #include <openssl/ssl.h>
       #include <curl/curl.h>
       #include <stdio.h>

       static CURLcode sslctx_function(CURL *curl, void *sslctx, void *pointer)
       {
         X509_STORE *store;
         X509 *cert = NULL;
         BIO *bio;
         char *mypem = pointer;
         /* get a BIO */
         bio = BIO_new_mem_buf(mypem, -1);
         /* use it to read the PEM formatted certificate from memory into an
          * X509 structure that SSL can use
          */
         PEM_read_bio_X509(bio, &cert, 0, NULL);
         if(!cert)
           printf("PEM_read_bio_X509 failed...\n");

         /* get a pointer to the X509 certificate store (which may be empty) */
         store = SSL_CTX_get_cert_store((SSL_CTX *)sslctx);

         /* add our certificate to this store */
         if(X509_STORE_add_cert(store, cert) == 0)
           printf("error adding certificate\n");

         /* decrease reference counts */
         X509_free(cert);
         BIO_free(bio);

         /* all set to go */
         return CURLE_OK;
       }

       int main(void)
       {
         CURL *curl;
         CURLcode result;
         /* CA cert in PEM format, replace the XXXs */
         const char *mypem =
           "-----BEGIN CERTIFICATE-----\n"
           "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
           "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
           "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
           "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
           "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
           "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n"
           "-----END CERTIFICATE-----\n";

         curl_global_init(CURL_GLOBAL_ALL);
         curl = curl_easy_init();

         curl_easy_setopt(curl, CURLOPT_SSLCERTTYPE, "PEM");
         curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 1L);
         curl_easy_setopt(curl, CURLOPT_URL, "https://www.example.com/");

         curl_easy_setopt(curl, CURLOPT_SSL_CTX_FUNCTION, *sslctx_function);
         curl_easy_setopt(curl, CURLOPT_SSL_CTX_DATA, mypem);
         result = curl_easy_perform(curl);
         if(result == CURLE_OK)
           printf("*** transfer succeeded ***\n");
         else
           printf("*** transfer failed ***\n");

         curl_easy_cleanup(curl);
         curl_global_cleanup();
         return (int)result;
       }

HISTORY
       Added in 7.11.0 for OpenSSL, in 7.42.0 for wolfSSL, in 7.54.0 for
       mbedTLS.

AVAILABILITY
       Added in curl 7.10.6

RETURN VALUE
       CURLE_OK if supported; or an error such as:

       CURLE_NOT_BUILT_IN - Not supported by the SSL backend

       CURLE_UNKNOWN_OPTION

SEE ALSO
       CURLOPT_SSLVERSION(3), CURLOPT_SSL_CTX_FUNCTION(3)

libcurl                           2026-09-02           CURLOPT_SSL_CTX_DATA(3)