CURLOPT_SSL_CTX_FUNCTION.3: added example

and removed erroneous reference to test case lib509

docs/libcurl/opts/CURLOPT_SSL_CTX_FUNCTION.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -50,18 +50,87 @@ callback's error code. Set the \fIuserptr\fP argument with the
 This function will get called on all new connections made to a server, during
 the SSL negotiation. The SSL_CTX pointer will be a new one every time.
 
-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
+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 a HTTPS request (example used in the lib509 test
-case).  See also the example section for a replacement of the key, certificate
-and trust file settings.
+change the actual URI of a HTTPS request.
 .SH DEFAULT
 NULL
 .SH PROTOCOLS
 All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
 .SH EXAMPLE
-TODO
+/* OpenSSL specific */
+
+#include <openssl/ssl.h>
+#include <curl/curl.h>
+#include <stdio.h>
+
+static CURLcode sslctx_function(CURL *curl, void *sslctx, void *parm)
+{
+  X509_STORE *store;
+  X509 *cert=NULL;
+  BIO *bio;
+  char *mypem = /* example CA cert PEM - shortened */
+    "-----BEGIN CERTIFICATE-----\n"
+    "MIIHPTCCBSWgAwIBAgIBADANBgkqhkiG9w0BAQQFADB5MRAwDgYDVQQKEwdSb290\n"
+    "IENBMR4wHAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMTGUNB\n"
+    "IENlcnQgU2lnbmluZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRA\n"
+    "Y2FjZXJ0Lm9yZzAeFw0wMzAzMzAxMjI5NDlaFw0zMzAzMjkxMjI5NDlaMHkxEDAO\n"
+    "GCSNe9FINSkYQKyTYOGWhlC0elnYjyELn8+CkcY7v2vcB5G5l1YjqrZslMZIBjzk\n"
+    "zk6q5PYvCdxTby78dOs6Y5nCpqyJvKeyRKANihDjbPIky/qbn3BHLt4Ui9SyIAmW\n"
+    "omTxJBzcoTWcFbLUvFUufQb1nA5V9FrWk9p2rSVzTMVD\n"\
+    "-----END CERTIFICATE-----\n";
+  /* get a BIO */
+  bio=BIO_new_mem_buf(mypem, -1);
+  /* use it to read the PEM formatted certificate from memory into an X509
+   * structure that SSL can use
+   */
+  PEM_read_bio_X509(bio, &cert, 0, NULL);
+  if(cert == NULL)
+    printf("PEM_read_bio_X509 failed...\n");
+
+  /* get a pointer to the X509 certificate store (which may be empty!) */
+  store=SSL_CTX_get_cert_store((SSL_CTX *)sslctx);
+
+  /* add our certificate to this store */
+  if(X509_STORE_add_cert(store, cert)==0)
+    printf("error adding certificate\n");
+
+  /* decrease reference counts */
+  X509_free(cert);
+  BIO_free(bio);
+
+  /* all set to go */
+  return CURLE_OK;
+}
+
+int main(void)
+{
+  CURL * ch;
+  CURLcode rv;
+
+  rv=curl_global_init(CURL_GLOBAL_ALL);
+  ch=curl_easy_init();
+  rv=curl_easy_setopt(ch, CURLOPT_SSLCERTTYPE, "PEM");
+  rv=curl_easy_setopt(ch, CURLOPT_SSL_VERIFYPEER, 1L);
+  rv=curl_easy_setopt(ch, CURLOPT_URL, "https://www.example.com/");
+
+  /* Retrieve page using cacerts' certificate -> will succeed
+   * load the certificate by installing a function doing the nescessary
+   * "modifications" to the SSL CONTEXT just before link init
+   */
+  rv=curl_easy_setopt(ch, CURLOPT_SSL_CTX_FUNCTION, *sslctx_function);
+  rv=curl_easy_perform(ch);
+  if(rv==CURLE_OK)
+    printf("*** transfer succeeded ***\n");
+  else
+    printf("*** transfer failed ***\n");
+
+  curl_easy_cleanup(ch);
+  curl_global_cleanup();
+  return rv;
+}
+
 .SH AVAILABILITY
 Added in 7.11.0 for OpenSSL. Added in 7.42.0 for wolfSSL/CyaSSL. Other SSL
 backends not supported.