---
name: "CURLOPT_PROXY_ISSUERCERT"
section: "3"
platform: "macos"
package: "curl"
version: "166.0.0.0.1"
release: "macOS 26.5"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_PROXY_ISSUERCERT"
---

# CURLOPT\_PROXY\_ISSUERCERT(3)

proxy issuer SSL certificate filename

## 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 *[CURLOPT\_PROXY\_SSL\_VERIFYPEER(3)](/CURLOPT_PROXY_SSL_VERIFYPEER/3.md)* 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)](/CURLOPT_PROXY_SSL_VERIFYPEER/3.md)* 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

## PROTOCOLS

All TLS-based protocols

## 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 7.71.0. This option is supported by the OpenSSL 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.

## SEE ALSO

[**CURLOPT\_ISSUERCERT**(3)](/CURLOPT_ISSUERCERT/3.md), [**CURLOPT\_PROXY\_SSL\_VERIFYHOST**(3)](/CURLOPT_PROXY_SSL_VERIFYHOST/3.md), [**CURLOPT\_PROXY\_SSL\_VERIFYPEER**(3)](/CURLOPT_PROXY_SSL_VERIFYPEER/3.md), [**CURLOPT\_SSL\_VERIFYHOST**(3)](/CURLOPT_SSL_VERIFYHOST/3.md), [**CURLOPT\_SSL\_VERIFYPEER**(3)](/CURLOPT_SSL_VERIFYPEER/3.md)