CURLOPT_PROXY_CAINFO - path to proxy Certificate Authority (CA) bundle

Added in curl 7.52.0

Built-in system specific

This option is for connecting to an HTTPS proxy, not an HTTPS server. Pass a char pointer 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 accessible file. This option is by default set to the system path where libcurl's CA certificate bundle is assumed to be stored, as established at build time. (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 uses 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 option. Using this option multiple times makes the last set string override the previous ones. Set it to NULL to disable its use again and switches back to internal default. The default value for this can be figured out with CURLINFO_CAINFO(3).

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_CAINFO, "/etc/certs/cabundle.pem"); res = curl_easy_perform(curl); curl_easy_cleanup(curl); } }

CURLOPT_PROXY_CAINFO - path to proxy Certificate Authority (CA) bundle

For TLS backends that do not support certificate files, the CURLOPT_PROXY_CAINFO(3) option is ignored. Refer to https://curl.se/docs/ssl-compared.html

This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc. All TLS backends support this option.

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).

CURLOPT_CAINFO(3), CURLOPT_CAINFO_BLOB(3), CURLOPT_CAPATH(3), CURLOPT_PROXY_CAINFO_BLOB(3), CURLOPT_PROXY_CAPATH(3), CURLOPT_PROXY_SSL_VERIFYHOST(3), CURLOPT_PROXY_SSL_VERIFYPEER(3), CURLOPT_SSL_VERIFYHOST(3), CURLOPT_SSL_VERIFYPEER(3) libcurl 2025-06-16 CURLOPT_PROXY_CAINFO(3)

#include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_CAINFO, char *path);