curl / libcurl / API / curl_easy_setopt / CURLOPT_PROXY_SSL_VERIFYHOST

CURLOPT_PROXY_SSL_VERIFYHOST explained

Name

CURLOPT_PROXY_SSL_VERIFYHOST - verify the proxy certificate's name against host

Synopsis

#include <curl/curl.h>
 
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_SSL_VERIFYHOST,
                          long verify);

Description

Pass a long set to 2L as asking curl to verify in the HTTPS proxy's certificate name fields against the proxy name.

This option determines whether libcurl verifies that the proxy cert contains the correct name for the name it is known as.

When CURLOPT_PROXY_SSL_VERIFYHOST is 2, the proxy certificate must indicate that the server is the proxy to which you meant to connect to, or the connection fails.

Curl considers the proxy the intended one when the Common Name field or a Subject Alternate Name field in the certificate matches the hostname in the proxy string which you told curl to use.

If verify value is set to 1:

In 7.28.0 and earlier: treated as a debug option of some sorts, not supported anymore due to frequently leading to programmer mistakes.

From 7.28.1 to 7.65.3: setting it to 1 made curl_easy_setopt return an error and leaving the flag untouched.

From 7.66.0: treats 1 and 2 the same.

When the verify value is 0L, the connection succeeds regardless of the names used in the certificate. Use that ability with caution.

See also CURLOPT_PROXY_SSL_VERIFYPEER to verify the digital signature of the proxy certificate.

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");
 
    /* Set the default value: strict name check please */
    curl_easy_setopt(curl, CURLOPT_PROXY_SSL_VERIFYHOST, 2L);
 
    curl_easy_perform(curl);
  }
}

Availability

Added in curl 7.52.0

Return value

Returns CURLE_OK if TLS is supported, and CURLE_UNKNOWN_OPTION if not.

If 1 is set as argument, CURLE_BAD_FUNCTION_ARGUMENT is returned.