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23 .TH CURLOPT_SSL_CTX_FUNCTION 3 "19 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
25 CURLOPT_SSL_CTX_FUNCTION \- SSL context callback for OpenSSL or wolfSSL/CyaSSL
28 #include <curl/curl.h>
30 CURLcode ssl_ctx_callback(CURL *curl, void *ssl_ctx, void *userptr);
32 CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
35 This option only works for libcurl powered by OpenSSL or wolfSSL/CyaSSL. If
36 libcurl was built against another SSL library this functionality is absent.
38 Pass a pointer to your callback function, which should match the prototype
41 This callback function gets called by libcurl just before the initialization
42 of an SSL connection after having processed all other SSL related options to
43 give a last chance to an application to modify the behaviour of the SSL
44 initialization. The \fIssl_ctx\fP parameter is actually a pointer to the SSL
45 library's \fISSL_CTX\fP. If an error is returned from the callback no attempt
46 to establish a connection is made and the perform operation will return the
47 callback's error code. Set the \fIuserptr\fP argument with the
48 \fICURLOPT_SSL_CTX_DATA(3)\fP option.
50 This function will get called on all new connections made to a server, during
51 the SSL negotiation. The SSL_CTX pointer will be a new one every time.
53 To use this properly, a non-trivial amount of knowledge of your SSL library is
54 necessary. For example, you can use this function to call library-specific
55 callbacks to add additional validation code for certificates, and even to
56 change the actual URI of a HTTPS request.
60 All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
63 /* OpenSSL specific */
65 #include <openssl/ssl.h>
66 #include <curl/curl.h>
69 static CURLcode sslctx_function(CURL *curl, void *sslctx, void *parm)
74 char *mypem = /* example CA cert PEM - shortened */
75 "-----BEGIN CERTIFICATE-----\n"
76 "MIIHPTCCBSWgAwIBAgIBADANBgkqhkiG9w0BAQQFADB5MRAwDgYDVQQKEwdSb290\n"
77 "IENBMR4wHAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMTGUNB\n"
78 "IENlcnQgU2lnbmluZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRA\n"
79 "Y2FjZXJ0Lm9yZzAeFw0wMzAzMzAxMjI5NDlaFw0zMzAzMjkxMjI5NDlaMHkxEDAO\n"
80 "GCSNe9FINSkYQKyTYOGWhlC0elnYjyELn8+CkcY7v2vcB5G5l1YjqrZslMZIBjzk\n"
81 "zk6q5PYvCdxTby78dOs6Y5nCpqyJvKeyRKANihDjbPIky/qbn3BHLt4Ui9SyIAmW\n"
82 "omTxJBzcoTWcFbLUvFUufQb1nA5V9FrWk9p2rSVzTMVD\n"\
83 "-----END CERTIFICATE-----\n";
85 bio=BIO_new_mem_buf(mypem, -1);
86 /* use it to read the PEM formatted certificate from memory into an X509
87 * structure that SSL can use
89 PEM_read_bio_X509(bio, &cert, 0, NULL);
91 printf("PEM_read_bio_X509 failed...\n");
93 /* get a pointer to the X509 certificate store (which may be empty!) */
94 store=SSL_CTX_get_cert_store((SSL_CTX *)sslctx);
96 /* add our certificate to this store */
97 if(X509_STORE_add_cert(store, cert)==0)
98 printf("error adding certificate\n");
100 /* decrease reference counts */
113 rv=curl_global_init(CURL_GLOBAL_ALL);
115 rv=curl_easy_setopt(ch, CURLOPT_SSLCERTTYPE, "PEM");
116 rv=curl_easy_setopt(ch, CURLOPT_SSL_VERIFYPEER, 1L);
117 rv=curl_easy_setopt(ch, CURLOPT_URL, "https://www.example.com/");
119 /* Retrieve page using cacerts' certificate -> will succeed
120 * load the certificate by installing a function doing the nescessary
121 * "modifications" to the SSL CONTEXT just before link init
123 rv=curl_easy_setopt(ch, CURLOPT_SSL_CTX_FUNCTION, *sslctx_function);
124 rv=curl_easy_perform(ch);
126 printf("*** transfer succeeded ***\n");
128 printf("*** transfer failed ***\n");
130 curl_easy_cleanup(ch);
131 curl_global_cleanup();
136 Added in 7.11.0 for OpenSSL. Added in 7.42.0 for wolfSSL/CyaSSL. Other SSL
137 backends not supported.
139 Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
141 .BR CURLOPT_SSL_CTX_DATA "(3), " CURLOPT_SSL_VERIFYPEER "(3), "