DragonFly On-Line Manual Pages
CURLOPT_SSL_CTX_FUNCTION(3) curl_easy_setopt options
CURLOPT_SSL_CTX_FUNCTION - SSL context callback for OpenSSL, wolfSSL or
CURLcode ssl_ctx_callback(CURL *curl, void *ssl_ctx, void *userptr);
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
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.
WARNING: If you are using DNS-over-HTTPS (DOH) via CURLOPT_DOH_URL(3)
then the CTX callback will also be called for those transfers and the
curl handle is set to an internal handle. This behavior is subject to
change. We recommend before performing your transfer set
CURLOPT_PRIVATE(3) on your curl handle so you can identify it in the
CTX callback. If you have a reason to modify DOH SSL context please let
us know on the curl-library mailing list because we are considering
removing this capability.
All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
See cacertinmem.c in docs/examples directory for usage example.
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.
CURLE_OK if supported; or an error such as:
CURLE_NOT_BUILT_IN - Not supported by the SSL backend
libcurl 7.76.0 March 4, 2021 CURLOPT_SSL_CTX_FUNCTION(3)