NAME

       CURLOPT_SSL_CTX_FUNCTION - SSL context callback for OpenSSL, wolfSSL or mbedTLS

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, wolfSSL or mbedTLS. 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
       behavior of the SSL initialization. The ssl_ctx parameter is actually a  pointer  to  the  SSL  library's
       SSL_CTX  for OpenSSL or wolfSSL, and a pointer to mbedtls_ssl_config for mbedTLS. 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 will point to a newly initialized object each time, but note the pointer may be the same as  from
       a prior call.

       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 an HTTPS request.

       WARNING:  The  CURLOPT_SSL_CTX_FUNCTION(3)  callback  allows  the  application to reach in and modify SSL
       details in the connection without libcurl itself knowing anything about it, which then  subsequently  can
       lead to libcurl unknowingly reusing SSL connections with different properties. To remedy this you may set
       CURLOPT_FORBID_REUSE(3) from the callback function.

DEFAULT

       NULL

PROTOCOLS

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

EXAMPLE

       See cacertinmem.c in docs/examples directory for usage example.

       https://curl.haxx.se/libcurl/c/cacertinmem.html

AVAILABILITY

       Added  in 7.11.0 for OpenSSL, in 7.42.0 for wolfSSL and in 7.54.0 for mbedTLS. Other SSL backends are not
       supported.

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_SSL_CTX_DATA(3), CURLOPT_SSL_VERIFYPEER(3),

libcurl 7.68.0                                    June 02, 2019                      CURLOPT_SSL_CTX_FUNCTION(3)