Tribblix: manual page: CURLOPT_DOH_SSL

CURLOPT_DOH_SSL_VERIFYPEER(3) Introduction to Library Functions

NAME

CURLOPT_DOH_SSL_VERIFYPEER - verify the DoH SSL certificate

SYNOPSIS

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DOH_SSL_VERIFYPEER,
long verify);

DESCRIPTION

Pass a long as parameter set to 1L to enable or 0L to disable.

This option tells curl to verify the authenticity of the DoH
(DNS-over-HTTPS) server's certificate. A value of 1 means curl
verifies; 0 (zero) means it does not.

This option is the DoH equivalent of CURLOPT_SSL_VERIFYPEER(3) and
only affects requests to the DoH server.

When negotiating a TLS or SSL connection, the server sends a
certificate indicating its identity. curl verifies whether the
certificate is authentic, i.e. that you can trust that the server is
who the certificate says it is. This trust is based on a chain of
digital signatures, rooted in certification authority (CA)
certificates you supply. curl uses a default bundle of CA
certificates (the path for that is determined at build time) and you
can specify alternate certificates with the CURLOPT_CAINFO(3) option
or the CURLOPT_CAPATH(3) option.

When CURLOPT_DOH_SSL_VERIFYPEER(3) is enabled, and the verification
fails to prove that the certificate is authentic, the connection
fails. When the option is zero, the peer certificate verification
succeeds regardless.

Authenticating the certificate is not enough to be sure about the
server. You typically also want to ensure that the server is the
server you mean to be talking to. Use CURLOPT_DOH_SSL_VERIFYHOST(3)
for that. The check that the hostname in the certificate is valid for
the hostname you are connecting to is done independently of the
CURLOPT_DOH_SSL_VERIFYPEER(3) option.

WARNING: disabling verification of the certificate allows bad guys to
man-in-the-middle the communication without you knowing it. Disabling
verification makes the communication insecure. Just having encryption
on a transfer is not enough as you cannot be sure that you are
communicating with the correct end-point.

DEFAULT

PROTOCOLS

This functionality affects all TLS based protocols: HTTPS, FTPS,
IMAPS, POP3S, SMTPS etc.

All TLS backends support this option.

EXAMPLE

int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

curl_easy_setopt(curl, CURLOPT_DOH_URL,
"https://cloudflare-dns.com/dns-query");

/* Disable certificate verification of the DoH server */
curl_easy_setopt(curl, CURLOPT_DOH_SSL_VERIFYPEER, 0L);

curl_easy_perform(curl);
}
}

AVAILABILITY

Added in curl 7.76.0

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).