NAME

       CURLOPT_SSL_CTX_FUNCTION - SSL context callback for OpenSSL or wolfSSL/CyaSSL

SYNOPSIS

       #include <curl/curl.h>

       CURLcode ssl_ctx_callback(CURL *curl, void *ssl_ctx, void *userptr);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
                                 ssl_ctx_callback);

DESCRIPTION

       This  option  only  works  for libcurl powered by OpenSSL or wolfSSL/CyaSSL. If libcurl was built against
       another SSL library this functionality is absent.

       Pass a pointer to your callback function, which should match the prototype shown above.

       This callback function gets called by libcurl just before the initialization of an SSL  connection  after
       having  processed  all  other  SSL  related options to give a last chance to an application to modify the
       behaviour of the SSL initialization. The ssl_ctx parameter is actually a pointer  to  the  SSL  library's
       SSL_CTX.  If  an error is returned from the callback no attempt to establish a connection is made and the
       perform  operation  will  return  the  callback's  error  code.  Set  the  userptr  argument   with   the
       CURLOPT_SSL_CTX_DATA(3) option.

       This  function  will  get called on all new connections made to a server, during the SSL negotiation. The
       SSL_CTX pointer will be a new one every time.

       To use this properly, a non-trivial amount of knowledge of your SSL library is  necessary.  For  example,
       you  can  use  this  function  to  call  library-specific callbacks to add additional validation code for
       certificates, and even to change the actual URI of a HTTPS request  (example  used  in  the  lib509  test
       case).  See also the example section for a replacement of the key, certificate and trust file settings.

DEFAULT

       NULL

PROTOCOLS

       All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

EXAMPLE

       TODO

AVAILABILITY

       Added in 7.11.0 for OpenSSL. Added in 7.42.0 for wolfSSL/CyaSSL. Other SSL backends not supported.

RETURN VALUE

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

SEE ALSO

       CURLOPT_SSL_CTX_DATA(3), CURLOPT_SSL_VERIFYPEER(3),