CURLOPT_PROXY_ISSUERCERT(3) Library Functions Manual
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.
The provided issuer certificate is used only for an issuer check against
the peer certificate; it is not validated or trusted by itself.
This option makes sense only when used in combination with the
CURLOPT_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
option, which is returned if the setup of the SSL/TLS session has failed
due to a mismatch with the issuer of peer certificate
(C) 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. only
This option works only with the following TLS backends: GnuTLS and
OpenSSL
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
/* using an HTTPS proxy */
curl_easy_setopt(curl, CURLOPT_PROXY, "https://proxy.example:443");
curl_easy_setopt(curl, CURLOPT_PROXY_ISSUERCERT, "/etc/certs/cacert.pem");
result = 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),
CURLOPT_PROXY_SSL_VERIFYPEER(3), CURLOPT_SSL_VERIFYHOST(3),
CURLOPT_SSL_VERIFYPEER(3)
libcurl 2026-10-18 CURLOPT_PROXY_ISSUERCERT(3)
curl 8.23.0 - Generated Sun Oct 18 18:02:49 CDT 2026