NAME

       CURLINFO_TLS_SESSION, CURLINFO_TLS_SSL_PTR - get TLS session info

SYNOPSIS

       #include <curl/curl.h>

       CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_TLS_SSL_PTR,
                                  struct curl_tlssessioninfo **session);

       /* if you need compatibility with libcurl < 7.48.0 use
          CURLINFO_TLS_SESSION instead: */

       CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_TLS_SESSION,
                                  struct curl_tlssessioninfo **session);

DESCRIPTION

       Pass  a  pointer  to a 'struct curl_tlssessioninfo *'.  The pointer will be initialized to
       refer to a 'struct curl_tlssessioninfo *' that will contain an  enum  indicating  the  SSL
       library  used  for  the  handshake  and  a  pointer to the respective internal TLS session
       structure of this underlying SSL library.

       This option may be useful for example to  extract  certificate  information  in  a  format
       convenient  for  further  processing,  such as manual validation. Refer to the LIMITATIONS
       section.

       struct curl_tlssessioninfo {
         curl_sslbackend backend;
         void *internals;
       };

       The backend  struct  member  is  one  of  the  defines  in  the  CURLSSLBACKEND_*  series:
       CURLSSLBACKEND_NONE    (when   built   without   TLS   support),   CURLSSLBACKEND_WOLFSSL,
       CURLSSLBACKEND_SECURETRANSPORT,        CURLSSLBACKEND_GNUTLS,        CURLSSLBACKEND_GSKIT,
       CURLSSLBACKEND_MBEDTLS,             CURLSSLBACKEND_NSS,            CURLSSLBACKEND_OPENSSL,
       CURLSSLBACKEND_SCHANNEL or CURLSSLBACKEND_MESALINK. (Note that the OpenSSL forks  are  all
       reported as just OpenSSL here.)

       The  internals  struct  member will point to a TLS library specific pointer for the active
       ("in use") SSL connection, with the following underlying types:

              GnuTLS gnutls_session_t

              gskit  gsk_handle

              NSS    PRFileDesc *

              OpenSSL
                     CURLINFO_TLS_SESSION: SSL_CTX *

                     CURLINFO_TLS_SSL_PTR: SSL *
       Since 7.48.0 the internals member can point to these other SSL backends as well:

              mbedTLS
                     mbedtls_ssl_context *

              Secure Channel
                     CtxtHandle *

              Secure Transport
                     SSLContext *

              wolfSSL
                     SSL *

              MesaLink
                     SSL *

       If the internals pointer is NULL then either the SSL backend  is  not  supported,  an  SSL
       session  has  not  yet been established or the connection is no longer associated with the
       easy handle (eg curl_easy_perform has returned).

LIMITATIONS

       This option has some limitations that could make it unsafe when it  comes  to  the  manual
       verification of certificates.

       This  option  only  retrieves  the  first in-use SSL session pointer for your easy handle,
       however your easy handle may have more than one in-use SSL session if using FTP over  SSL.
       That  is because the FTP protocol has a control channel and a data channel and one or both
       may be over SSL. Currently there is no  way  to  retrieve  a  second  in-use  SSL  session
       associated with an easy handle.

       This  option  has  not  been  thoroughly  tested  with  plaintext  protocols  that  can be
       upgraded/downgraded to/from SSL: FTP, SMTP, POP3, IMAP when used with  CURLOPT_USE_SSL(3).
       Though  you will be able to retrieve the SSL pointer, it's possible that before you can do
       that data (including auth) may have already been sent  over  a  connection  after  it  was
       upgraded.

       Renegotiation.  If  unsafe renegotiation or renegotiation in a way that the certificate is
       allowed to change is allowed by your SSL library this may occur and  the  certificate  may
       change,  and  data  may continue to be sent or received after renegotiation but before you
       are able  to  get  the  (possibly)  changed  SSL  pointer,  with  the  (possibly)  changed
       certificate information.

       If  you are using OpenSSL or wolfSSL then CURLOPT_SSL_CTX_FUNCTION(3) can be used to set a
       certificate verification callback in the CTX. That is safer than using this option to poll
       for  certificate  changes  and  does  not  suffer from any of the problems above. There is
       currently no way in libcurl to set a verification callback for the other SSL backends.

       How are you using this option? Are you affected by any of these limitations?   Please  let
       us know by making a comment at https://github.com/curl/curl/issues/685

PROTOCOLS

       All TLS-based

EXAMPLE

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

       CURL *curl;
       static size_t wf(void *ptr, size_t size, size_t nmemb, void *stream)
       {
         const struct curl_tlssessioninfo *info = NULL;
         CURLcode res = curl_easy_getinfo(curl, CURLINFO_TLS_SSL_PTR, &info);
         if(info && !res) {
           if(CURLSSLBACKEND_OPENSSL == info->backend) {
              printf("OpenSSL ver. %s\n", SSL_get_version((SSL*)info->internals));
           }
         }
         return size * nmemb;
       }

       int main(int argc, char** argv)
       {
         CURLcode res;
         curl = curl_easy_init();
         if(curl) {
           curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
           curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, wf);
           res = curl_easy_perform(curl);
           curl_easy_cleanup(curl);
         }
         return res;
       }

AVAILABILITY

       Added in 7.48.0.

       This  option supersedes CURLINFO_TLS_SESSION(3) which was added in 7.34.0.  This option is
       exactly the same as that option except in the case of OpenSSL.

RETURN VALUE

       Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

SEE ALSO

       curl_easy_getinfo(3), curl_easy_setopt(3), CURLINFO_TLS_SESSION(3),