CURLOPT_SSL_CTX_FUNCTION(3)

1CURLOPT_SSL_CTX_FUNCTION(3)curl_easy_setopt optionsCURLOPT_SSL_CTX_FUNCTION(3)
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NAME

6       CURLOPT_SSL_CTX_FUNCTION  -  SSL  context  callback  for OpenSSL, wolf‐
7       SSL/CyaSSL or mbedTLS
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SYNOPSIS

10       #include <curl/curl.h>
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12       CURLcode ssl_ctx_callback(CURL *curl, void *ssl_ctx, void *userptr);
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14       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
15                                 ssl_ctx_callback);
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DESCRIPTION

18       This option only works for libcurl powered by  OpenSSL,  wolfSSL/CyaSSL
19       or mbedTLS. If libcurl was built against another SSL library this func‐
20       tionality is absent.
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22       Pass a pointer to your callback function, which should match the proto‐
23       type shown above.
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25       This  callback function gets called by libcurl just before the initial‐
26       ization of an SSL connection  after  having  processed  all  other  SSL
27       related  options  to give a last chance to an application to modify the
28       behavior of the SSL initialization. The ssl_ctx parameter is actually a
29       pointer to the SSL library's SSL_CTX for OpenSSL or wolfSSL/CyaSSL, and
30       a pointer to mbedtls_ssl_config for mbedTLS. If an  error  is  returned
31       from  the callback no attempt to establish a connection is made and the
32       perform operation will  return  the  callback's  error  code.  Set  the
33       userptr argument with the CURLOPT_SSL_CTX_DATA(3) option.
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35       This  function will get called on all new connections made to a server,
36       during the SSL negotiation. The ssl_ctx will point to a newly  initial‐
37       ized  object  each time, but note the pointer may be the same as from a
38       prior call.
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40       To use this properly, a non-trivial amount of  knowledge  of  your  SSL
41       library  is  necessary.  For example, you can use this function to call
42       library-specific callbacks to add additional validation code  for  cer‐
43       tificates, and even to change the actual URI of an HTTPS request.
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45       WARNING:  The  CURLOPT_SSL_CTX_FUNCTION(3) callback allows the applica‐
46       tion to reach in and modify  SSL  details  in  the  connection  without
47       libcurl  itself  knowing anything about it, which then subsequently can
48       lead to libcurl unknowingly  reusing  SSL  connections  with  different
49       properties. To remedy this you may set CURLOPT_FORBID_REUSE(3) from the
50       callback function.
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DEFAULT

53       NULL
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PROTOCOLS

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

59       See cacertinmem.c in docs/examples directory for usage example.
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61       https://curl.haxx.se/libcurl/c/cacertinmem.html
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AVAILABILITY

64       Added in 7.11.0 for OpenSSL. Added in 7.42.0 for wolfSSL/CyaSSL.  Added
65       in 7.54.0 for mbedTLS. Other SSL backends not supported.
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RETURN VALUE

68       CURLE_OK if supported; or an error such as:
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70       CURLE_NOT_BUILT_IN - Not supported by the SSL backend
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72       CURLE_UNKNOWN_OPTION
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