mirror of
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e3fe020089
Remove the PROTOCOLS section from the source files completely and instead generate them based on the header data in the curldown files. It also generates TLS backend information for options marked for TLS as protocol. Closes #13175
169 lines
5.3 KiB
Markdown
169 lines
5.3 KiB
Markdown
---
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c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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Title: CURLOPT_SSL_CTX_FUNCTION
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Section: 3
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Source: libcurl
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See-also:
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- CURLOPT_SSL_CTX_DATA (3)
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- CURLOPT_SSL_VERIFYPEER (3)
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- CURLOPT_CAINFO (3)
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Protocol:
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- TLS
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TLS-backend:
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- OpenSSL
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- wolfSSL
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- mbedTLS
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- BearSSL
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---
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# NAME
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CURLOPT_SSL_CTX_FUNCTION - SSL context callback
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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CURLcode ssl_ctx_callback(CURL *curl, void *ssl_ctx, void *clientp);
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
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ssl_ctx_callback);
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~~~
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# DESCRIPTION
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Pass a pointer to your callback function, which should match the prototype
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shown above.
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This callback function gets called by libcurl just before the initialization
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of an SSL connection after having processed all other SSL related options to
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give a last chance to an application to modify the behavior of the SSL
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initialization. The *ssl_ctx* parameter is a pointer to the SSL library's
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*SSL_CTX* for OpenSSL or wolfSSL, a pointer to *mbedtls_ssl_config* for
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mbedTLS or a pointer to *br_ssl_client_context* for BearSSL. If an error is
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returned from the callback no attempt to establish a connection is made and
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the perform operation returns the callback's error code. Set the *clientp*
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argument passed in to this callback with the CURLOPT_SSL_CTX_DATA(3) option.
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This function gets called for all new connections made to a server, during the
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SSL negotiation. While *ssl_ctx* points to a newly initialized object each
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time, the pointer may still be the same as in a prior call.
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To use this callback, a non-trivial amount of knowledge of your SSL library is
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necessary. For example, you can use this function to call library-specific
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callbacks to add additional validation code for certificates, and even to
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change the actual URI of an HTTPS request.
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For OpenSSL, asynchronous certificate verification via *SSL_set_retry_verify*
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is supported. (Added in 8.3.0)
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The CURLOPT_SSL_CTX_FUNCTION(3) callback allows the application to reach in
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and modify SSL details in the connection without libcurl itself knowing
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anything about it, which then subsequently can lead to libcurl unknowingly
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reusing SSL connections with different properties. To remedy this you may set
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CURLOPT_FORBID_REUSE(3) from the callback function.
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If you are using DNS-over-HTTPS (DoH) via CURLOPT_DOH_URL(3) then this
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callback is also called for those transfers and the curl handle is set to an
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internal handle. **This behavior is subject to change.** We recommend setting
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CURLOPT_PRIVATE(3) on your curl handle so you can identify it correctly in the
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context callback. If you have a reason to modify DoH SSL context please let us
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know on the curl-library mailing list because we are considering removing this
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capability.
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libcurl does not guarantee the lifetime of the passed in object once this
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callback function has returned. Your application must not assume that it can
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keep using the SSL context or data derived from it once this function is
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completed.
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# DEFAULT
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NULL
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# EXAMPLE
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~~~c
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/* OpenSSL specific */
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#include <openssl/ssl.h>
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#include <curl/curl.h>
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#include <stdio.h>
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static CURLcode sslctx_function(CURL *curl, void *sslctx, void *parm)
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{
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X509_STORE *store;
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X509 *cert = NULL;
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BIO *bio;
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char *mypem = parm;
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/* get a BIO */
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bio = BIO_new_mem_buf(mypem, -1);
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/* use it to read the PEM formatted certificate from memory into an
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* X509 structure that SSL can use
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*/
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PEM_read_bio_X509(bio, &cert, 0, NULL);
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if(!cert)
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printf("PEM_read_bio_X509 failed...\n");
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/* get a pointer to the X509 certificate store (which may be empty) */
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store = SSL_CTX_get_cert_store((SSL_CTX *)sslctx);
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/* add our certificate to this store */
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if(X509_STORE_add_cert(store, cert) == 0)
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printf("error adding certificate\n");
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/* decrease reference counts */
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X509_free(cert);
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BIO_free(bio);
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/* all set to go */
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return CURLE_OK;
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}
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int main(void)
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{
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CURL *ch;
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CURLcode rv;
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char *mypem = /* example CA cert PEM - shortened */
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"-----BEGIN CERTIFICATE-----\n"
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"MIIHPTCCBSWgAwIBAgIBADANBgkqhkiG9w0BAQQFADB5MRAwDgYDVQQKEwdSb290\n"
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"IENBMR4wHAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMTGUNB\n"
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"IENlcnQgU2lnbmluZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRA\n"
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"Y2FjZXJ0Lm9yZzAeFw0wMzAzMzAxMjI5NDlaFw0zMzAzMjkxMjI5NDlaMHkxEDAO\n"
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"GCSNe9FINSkYQKyTYOGWhlC0elnYjyELn8+CkcY7v2vcB5G5l1YjqrZslMZIBjzk\n"
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"zk6q5PYvCdxTby78dOs6Y5nCpqyJvKeyRKANihDjbPIky/qbn3BHLt4Ui9SyIAmW\n"
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"omTxJBzcoTWcFbLUvFUufQb1nA5V9FrWk9p2rSVzTMVD\n"
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"-----END CERTIFICATE-----\n";
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curl_global_init(CURL_GLOBAL_ALL);
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ch = curl_easy_init();
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curl_easy_setopt(ch, CURLOPT_SSLCERTTYPE, "PEM");
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curl_easy_setopt(ch, CURLOPT_SSL_VERIFYPEER, 1L);
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curl_easy_setopt(ch, CURLOPT_URL, "https://www.example.com/");
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curl_easy_setopt(ch, CURLOPT_SSL_CTX_FUNCTION, *sslctx_function);
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curl_easy_setopt(ch, CURLOPT_SSL_CTX_DATA, mypem);
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rv = curl_easy_perform(ch);
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if(!rv)
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printf("*** transfer succeeded ***\n");
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else
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printf("*** transfer failed ***\n");
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curl_easy_cleanup(ch);
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curl_global_cleanup();
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return rv;
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}
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~~~
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# AVAILABILITY
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OpenSSL (added in 7.11.0), wolfSSL (added in 7.42.0), mbedTLS (added in
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7.54.0) or BearSSL (added in 7.83.0)
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# RETURN VALUE
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CURLE_OK if supported; or an error such as:
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CURLE_NOT_BUILT_IN - Not supported by the SSL backend
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