CURLOPT_PROXY_ISSUERCERT(3) Library Functions ManualCURLOPT_PROXY_ISSUERCERT(3)
NAME
CURLOPT_PROXY_ISSUERCERT - proxy issuer SSL certificate filename
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_ISSUERCERT, char *file);
DESCRIPTION
Pass a char pointer to a null-terminated string naming a file holding a
CA certificate in PEM format. If the option is set, an additional check
against the peer certificate is performed to verify the issuer of the
HTTPS proxy is indeed the one associated with the certificate provided
by the option. This additional check is useful in multi-level PKI where
one needs to enforce that the peer certificate is from a specific branch
of the tree.
This option makes sense only when used in combination with the CUR-
LOPT_PROXY_SSL_VERIFYPEER(3) option. Otherwise, the result of the check
is not considered as failure.
A specific error code (CURLE_SSL_ISSUER_ERROR) is defined with the op-
tion, which is returned if the setup of the SSL/TLS session has failed
due to a mismatch with the issuer of peer certificate (CUR-
LOPT_PROXY_SSL_VERIFYPEER(3) has to be set too for the check to fail).
The application does not have to keep the string around after setting
this option.
Using this option multiple times makes the last set string override the
previous ones. Set it to NULL to disable its use again.
DEFAULT
NULL
PROTOCOLS
This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS,
POP3S, SMTPS etc.
This option works only with the following TLS backends: GnuTLS and
OpenSSL
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode res;
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
/* using an HTTPS proxy */
curl_easy_setopt(curl, CURLOPT_PROXY, "https://localhost:443");
curl_easy_setopt(curl, CURLOPT_PROXY_ISSUERCERT, "/etc/certs/cacert.pem");
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
AVAILABILITY
Added in curl 7.71.0
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_ISSUERCERT(3), CURLOPT_PROXY_SSL_VERIFYHOST(3), CUR-
LOPT_PROXY_SSL_VERIFYPEER(3), CURLOPT_SSL_VERIFYHOST(3), CUR-
LOPT_SSL_VERIFYPEER(3)
libcurl 2026-07-12 CURLOPT_PROXY_ISSUERCERT(3)
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