---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_PROXY_ISSUERCERT_BLOB
Section: 3
Source: libcurl
See-also:
  - CURLOPT_ISSUERCERT_BLOB (3)
  - CURLOPT_PROXY_SSL_VERIFYHOST (3)
  - CURLOPT_PROXY_SSL_VERIFYPEER (3)
  - CURLOPT_SSL_VERIFYHOST (3)
  - CURLOPT_SSL_VERIFYPEER (3)
Protocol:
  - TLS
TLS-backend:
  - OpenSSL
Added-in: 7.71.0
---

# NAME

CURLOPT_PROXY_ISSUERCERT_BLOB - proxy issuer SSL certificate from memory blob

# SYNOPSIS

~~~c
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_ISSUERCERT_BLOB,
                          struct curl_blob *blob);
~~~

# DESCRIPTION

Pass a pointer to a curl_blob struct, which contains information (pointer and
size) about a memory block with binary data of 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 should be 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).

If the blob is initialized with the flags member of struct curl_blob set to
CURL_BLOB_COPY, the application does not have to keep the buffer around after
setting this.

This option is an alternative to CURLOPT_PROXY_ISSUERCERT(3) which
instead expects a filename as input.

# DEFAULT

NULL

# %PROTOCOLS%

# EXAMPLE

~~~c

static char *certificateData; /* point to the data */
static size_t filesize; /* size of the data */

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    struct curl_blob blob;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    /* using an HTTPS proxy */
    curl_easy_setopt(curl, CURLOPT_PROXY, "https://proxy.example:443");
    blob.data = certificateData;
    blob.len = filesize;
    blob.flags = CURL_BLOB_COPY;
    curl_easy_setopt(curl, CURLOPT_PROXY_ISSUERCERT_BLOB, &blob);
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}
~~~

# %AVAILABILITY%

# 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).
