**************************************************************************
* _ _ ____ _
* Project ___| | | | _ \| |
* / __| | | | |_) | |
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
*
* This software is licensed as described in the file COPYING, which
* you should have received as part of this distribution. The terms
* are also available at https://curl.haxx.se/docs/copyright.html.
*
* You may opt to use, copy, modify, merge, publish, distribute and/or sell
* copies of the Software, and permit persons to whom the Software is
* furnished to do so, under the terms of the COPYING file.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
**************************************************************************

CURLOPT_PROXY_CAPATH - specify directory holding proxy CA certificates #include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_CAPATH, char *capath); Pass a char * to a null-terminated string naming a directory holding multiple CA certificates to verify the HTTPS proxy with. If libcurl is built against OpenSSL, the certificate directory must be prepared using the openssl c_rehash utility. This makes sense only when CURLOPT_PROXY_SSL_VERIFYPEER(3) is enabled (which it is by default). The application does not have to keep the string around after setting this option. NULL Everything used over an HTTPS proxy

CURL *curl = curl_easy_init();
if(curl) {
 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_CAPATH, "/etc/cert-dir");
 ret = curl_easy_perform(curl);
 curl_easy_cleanup(curl);
}

Added in 7.52.0 This option is supported by the OpenSSL, GnuTLS, and mbedTLS (since 7.56.0) backends. The NSS backend provides the option only for backward compatibility. CURLE_OK if supported; or an error such as: CURLE_NOT_BUILT_IN - Not supported by the SSL backend CURLE_UNKNOWN_OPTION CURLE_OUT_OF_MEMORY CURLOPT_PROXY_CAINFO "(3), " CURLOPT_CAINFO "(3), " CURLOPT_PROXY_SSL_VERIFYHOST "(3), " CURLOPT_STDERR "(3), " CURLOPT_DEBUGFUNCTION "(3), "