docs/libcurl/opts/CURLOPT_SSL_CTX_FUNCTION.3 - platform/external/curl - Git at Google

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 .\" *
 .\" * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
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 .\" * you should have received as part of this distribution. The terms
 .\" * are also available at https://curl.se/docs/copyright.html.
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 .\" * copies of the Software, and permit persons to whom the Software is
 .\" * furnished to do so, under the terms of the COPYING file.
 .\" *
 .\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 .\" * KIND, either express or implied.
 .\" *
 .\" **************************************************************************
 .\"
 .TH CURLOPT_SSL_CTX_FUNCTION 3 "July 26, 2021" "libcurl 7.80.0" "curl_easy_setopt options"

 .SH NAME
 CURLOPT_SSL_CTX_FUNCTION \- SSL context callback for OpenSSL, wolfSSL or mbedTLS
 .SH SYNOPSIS
 .nf
 #include <curl/curl.h>

 CURLcode ssl_ctx_callback(CURL *curl, void *ssl_ctx, void *userptr);

 CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
                           ssl_ctx_callback);
 .SH DESCRIPTION
 This option only works for libcurl powered by OpenSSL, wolfSSL or mbedTLS. If
 libcurl was built against another SSL library this functionality is absent.

 Pass a pointer to your callback function, which should match the prototype
 shown above.

 This callback function gets called by libcurl just before the initialization
 of an SSL connection after having processed all other SSL related options to
 give a last chance to an application to modify the behavior of the SSL
 initialization. The \fIssl_ctx\fP parameter is actually a pointer to the SSL
 library's \fISSL_CTX\fP for OpenSSL or wolfSSL, and a pointer to
 \fImbedtls_ssl_config\fP for mbedTLS. If an error is returned from the
 callback no attempt to establish a connection is made and the perform
 operation will return the callback's error code. Set the \fIuserptr\fP
 argument with the \fICURLOPT_SSL_CTX_DATA(3)\fP option.

 This function will get called on all new connections made to a server, during
 the SSL negotiation. The \fIssl_ctx\fP will point to a newly initialized object
 each time, but note the pointer may be the same as from a prior call.

 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 an HTTPS request.

 WARNING: The \fICURLOPT_SSL_CTX_FUNCTION(3)\fP callback allows the application
 to reach in and modify SSL details in the connection without libcurl itself
 knowing anything about it, which then subsequently can lead to libcurl
 unknowingly reusing SSL connections with different properties. To remedy this
 you may set \fICURLOPT_FORBID_REUSE(3)\fP from the callback function.

 WARNING: If you are using DNS-over-HTTPS (DoH) via \fICURLOPT_DOH_URL(3)\fP
 then the CTX callback will also be called for those transfers and the curl
 handle is set to an internal handle. \fBThis behavior is subject to change.\fP
 We recommend before performing your transfer set \fICURLOPT_PRIVATE(3)\fP on
 your curl handle so you can identify it in the CTX callback. If you have a
 reason to modify DoH SSL context please let us know on the curl-library mailing
 list because we are considering removing this capability.
 .SH DEFAULT
 NULL
 .SH PROTOCOLS
 All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
 .SH EXAMPLE
 .nf
 /* 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 = parm;
   /* 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;
   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";

   curl_global_init(CURL_GLOBAL_ALL);
   ch = curl_easy_init();

   curl_easy_setopt(ch, CURLOPT_SSLCERTTYPE, "PEM");
   curl_easy_setopt(ch, CURLOPT_SSL_VERIFYPEER, 1L);
   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 necessary
    * "modifications" to the SSL CONTEXT just before link init
    */
   curl_easy_setopt(ch, CURLOPT_SSL_CTX_FUNCTION, *sslctx_function);
   curl_easy_setopt(ch, CURLOPT_SSL_CTX_DATA, mypem);
   rv = curl_easy_perform(ch);
   if(!rv)
     printf("*** transfer succeeded ***\\n");
   else
     printf("*** transfer failed ***\\n");

   curl_easy_cleanup(ch);
   curl_global_cleanup();
   return rv;
 }
 .fi
 .SH AVAILABILITY
 Added in 7.11.0 for OpenSSL, in 7.42.0 for wolfSSL and in 7.54.0 for
 mbedTLS. Other SSL backends are not supported.
 .SH RETURN VALUE
 CURLE_OK if supported; or an error such as:

 CURLE_NOT_BUILT_IN - Not supported by the SSL backend

 CURLE_UNKNOWN_OPTION
 .SH "SEE ALSO"
 .BR CURLOPT_SSL_CTX_DATA "(3), " CURLOPT_SSL_VERIFYPEER "(3), "
	.\" **************************************************************************
	.\" * _ _ ____ _
	.\" * Project ___\| \| \| \| _ \\| \|
	.\" * / __\| \| \| \| \|_) \| \|
	.\" * \| (__\| \|_\| \| _ <\| \|___
	.\" * \___\|\___/\|_\| \_\_____\|
	.\" *
	.\" * Copyright (C) 1998 - 2021, 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
	.\" * are also available at https://curl.se/docs/copyright.html.
	.\" *
	.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
	.\" * copies of the Software, and permit persons to whom the Software is
	.\" * furnished to do so, under the terms of the COPYING file.
	.\" *
	.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
	.\" * KIND, either express or implied.
	.\" *
	.\" **************************************************************************
	.\"
	.TH CURLOPT_SSL_CTX_FUNCTION 3 "July 26, 2021" "libcurl 7.80.0" "curl_easy_setopt options"

	.SH NAME
	CURLOPT_SSL_CTX_FUNCTION \- SSL context callback for OpenSSL, wolfSSL or mbedTLS
	.SH SYNOPSIS
	.nf
	#include <curl/curl.h>

	CURLcode ssl_ctx_callback(CURL curl, void ssl_ctx, void *userptr);

	CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CTX_FUNCTION,
	ssl_ctx_callback);
	.SH DESCRIPTION
	This option only works for libcurl powered by OpenSSL, wolfSSL or mbedTLS. If
	libcurl was built against another SSL library this functionality is absent.

	Pass a pointer to your callback function, which should match the prototype
	shown above.

	This callback function gets called by libcurl just before the initialization
	of an SSL connection after having processed all other SSL related options to
	give a last chance to an application to modify the behavior of the SSL
	initialization. The \fIssl_ctx\fP parameter is actually a pointer to the SSL
	library's \fISSL_CTX\fP for OpenSSL or wolfSSL, and a pointer to
	\fImbedtls_ssl_config\fP for mbedTLS. If an error is returned from the
	callback no attempt to establish a connection is made and the perform
	operation will return the callback's error code. Set the \fIuserptr\fP
	argument with the \fICURLOPT_SSL_CTX_DATA(3)\fP option.

	This function will get called on all new connections made to a server, during
	the SSL negotiation. The \fIssl_ctx\fP will point to a newly initialized object
	each time, but note the pointer may be the same as from a prior call.

	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 an HTTPS request.

	WARNING: The \fICURLOPT_SSL_CTX_FUNCTION(3)\fP callback allows the application
	to reach in and modify SSL details in the connection without libcurl itself
	knowing anything about it, which then subsequently can lead to libcurl
	unknowingly reusing SSL connections with different properties. To remedy this
	you may set \fICURLOPT_FORBID_REUSE(3)\fP from the callback function.

	WARNING: If you are using DNS-over-HTTPS (DoH) via \fICURLOPT_DOH_URL(3)\fP
	then the CTX callback will also be called for those transfers and the curl
	handle is set to an internal handle. \fBThis behavior is subject to change.\fP
	We recommend before performing your transfer set \fICURLOPT_PRIVATE(3)\fP on
	your curl handle so you can identify it in the CTX callback. If you have a
	reason to modify DoH SSL context please let us know on the curl-library mailing
	list because we are considering removing this capability.
	.SH DEFAULT
	NULL
	.SH PROTOCOLS
	All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
	.SH EXAMPLE
	.nf
	/* 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 = parm;
	/* 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;
	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";

	curl_global_init(CURL_GLOBAL_ALL);
	ch = curl_easy_init();

	curl_easy_setopt(ch, CURLOPT_SSLCERTTYPE, "PEM");
	curl_easy_setopt(ch, CURLOPT_SSL_VERIFYPEER, 1L);
	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 necessary
	* "modifications" to the SSL CONTEXT just before link init
	*/
	curl_easy_setopt(ch, CURLOPT_SSL_CTX_FUNCTION, *sslctx_function);
	curl_easy_setopt(ch, CURLOPT_SSL_CTX_DATA, mypem);
	rv = curl_easy_perform(ch);
	if(!rv)
	printf("* transfer succeeded *\\n");
	else
	printf("* transfer failed *\\n");

	curl_easy_cleanup(ch);
	curl_global_cleanup();
	return rv;
	}
	.fi
	.SH AVAILABILITY
	Added in 7.11.0 for OpenSSL, in 7.42.0 for wolfSSL and in 7.54.0 for
	mbedTLS. Other SSL backends are not supported.
	.SH RETURN VALUE
	CURLE_OK if supported; or an error such as:

	CURLE_NOT_BUILT_IN - Not supported by the SSL backend

	CURLE_UNKNOWN_OPTION
	.SH "SEE ALSO"
	.BR CURLOPT_SSL_CTX_DATA "(3), " CURLOPT_SSL_VERIFYPEER "(3), "