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                     23: .TH CURLOPT_SSL_CTX_FUNCTION 3 "June 02, 2019" "libcurl 7.70.0" "curl_easy_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLOPT_SSL_CTX_FUNCTION \- SSL context callback for OpenSSL, wolfSSL or mbedTLS
                     27: .SH SYNOPSIS
                     28: .nf
                     29: #include <curl/curl.h>
                     30: 
                     31: CURLcode ssl_ctx_callback(CURL *curl, void *ssl_ctx, void *userptr);
                     32: 
                     33: CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
                     34:                           ssl_ctx_callback);
                     35: .SH DESCRIPTION
                     36: This option only works for libcurl powered by OpenSSL, wolfSSL or mbedTLS. If
                     37: libcurl was built against another SSL library this functionality is absent.
                     38: 
                     39: Pass a pointer to your callback function, which should match the prototype
                     40: shown above.
                     41: 
                     42: This callback function gets called by libcurl just before the initialization
                     43: of an SSL connection after having processed all other SSL related options to
                     44: give a last chance to an application to modify the behavior of the SSL
                     45: initialization. The \fIssl_ctx\fP parameter is actually a pointer to the SSL
                     46: library's \fISSL_CTX\fP for OpenSSL or wolfSSL, and a pointer to
                     47: \fImbedtls_ssl_config\fP for mbedTLS. If an error is returned from the
                     48: callback no attempt to establish a connection is made and the perform
                     49: operation will return the callback's error code. Set the \fIuserptr\fP
                     50: argument with the \fICURLOPT_SSL_CTX_DATA(3)\fP option.
                     51: 
                     52: This function will get called on all new connections made to a server, during
                     53: the SSL negotiation. The \fIssl_ctx\fP will point to a newly initialized object
                     54: each time, but note the pointer may be the same as from a prior call.
                     55: 
                     56: To use this properly, a non-trivial amount of knowledge of your SSL library is
                     57: necessary. For example, you can use this function to call library-specific
                     58: callbacks to add additional validation code for certificates, and even to
                     59: change the actual URI of an HTTPS request.
                     60: 
                     61: WARNING: The \fICURLOPT_SSL_CTX_FUNCTION(3)\fP callback allows the application
                     62: to reach in and modify SSL details in the connection without libcurl itself
                     63: knowing anything about it, which then subsequently can lead to libcurl
                     64: unknowingly reusing SSL connections with different properties. To remedy this
                     65: you may set \fICURLOPT_FORBID_REUSE(3)\fP from the callback function.
                     66: .SH DEFAULT
                     67: NULL
                     68: .SH PROTOCOLS
                     69: All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
                     70: .SH EXAMPLE
                     71: See cacertinmem.c in docs/examples directory for usage example.
                     72: 
                     73: https://curl.haxx.se/libcurl/c/cacertinmem.html
                     74: .SH AVAILABILITY
                     75: Added in 7.11.0 for OpenSSL, in 7.42.0 for wolfSSL and in 7.54.0 for
                     76: mbedTLS. Other SSL backends are not supported.
                     77: .SH RETURN VALUE
                     78: CURLE_OK if supported; or an error such as:
                     79: 
                     80: CURLE_NOT_BUILT_IN - Not supported by the SSL backend
                     81: 
                     82: CURLE_UNKNOWN_OPTION
                     83: .SH "SEE ALSO"
                     84: .BR CURLOPT_SSL_CTX_DATA "(3), " CURLOPT_SSL_VERIFYPEER "(3), "