---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_PROXY_ISSUERCERT
Section: 3
Source: libcurl
See-also:
  - CURLOPT_ISSUERCERT (3)
  - CURLOPT_PROXY_SSL_VERIFYHOST (3)
  - CURLOPT_PROXY_SSL_VERIFYPEER (3)
  - CURLOPT_SSL_VERIFYHOST (3)
  - CURLOPT_SSL_VERIFYPEER (3)
Protocol:
  - TLS
TLS-backend:
  - OpenSSL
  - GnuTLS
---

# NAME

CURLOPT_PROXY_ISSUERCERT - proxy issuer SSL certificate filename

# SYNOPSIS

~~~c
#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
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
(CURLOPT_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.

# DEFAULT

NULL

# EXAMPLE

~~~c
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 7.71.0. This option is supported by the OpenSSL and GnuTLS backends.

# RETURN VALUE

Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or
CURLE_OUT_OF_MEMORY if there was insufficient heap space.