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),