Section: curl_easy_setopt options (3)
Updated: June 25, 2020
CURLOPT_PROXY_CAINFO - path to proxy Certificate Authority (CA) bundle
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_CAINFO, char *path);
This option is for connecting to an HTTPS proxy, not an HTTPS server.
Pass a char * to a null-terminated string naming a file holding one or more
certificates to verify the HTTPS proxy with.
If CURLOPT_PROXY_SSL_VERIFYPEER(3) is zero and you avoid verifying the
server's certificate, CURLOPT_PROXY_CAINFO(3) need not even indicate an
This option is by default set to the system path where libcurl's cacert bundle
is assumed to be stored, as established at build time.
If curl is built against the NSS SSL library, the NSS PEM PKCS#11 module
(libnsspem.so) needs to be available for this option to work properly.
(iOS and macOS only) If curl is built against Secure Transport, then this
option is supported for backward compatibility with other SSL engines, but it
should not be set. If the option is not set, then curl will use the
certificates in the system and user Keychain to verify the peer, which is the
preferred method of verifying the peer's certificate chain.
The application does not have to keep the string around after setting this
Built-in system specific
Used with HTTPS proxy
CURL *curl = curl_easy_init();
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_CAINFO, "/etc/certs/cabundle.pem");
ret = curl_easy_perform(curl);
Added in 7.52.0
For TLS backends that don't support certificate files, the
CURLOPT_PROXY_CAINFO(3) option is ignored. Refer to
Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or
CURLE_OUT_OF_MEMORY if there was insufficient heap space.