CURLOPT_PROXY_SERVICE_NAME man page
CURLOPT_PROXY_SERVICE_NAME — proxy authentication service name
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_SERVICE_NAME, char *name);
Pass a char * as parameter to a string holding the name of the service. The default service name is "HTTP" for HTTP based proxies and "rcmd" for SOCKS5. This option allows you to change it.
The application does not have to keep the string around after setting this option.
All network protocols
Added in 7.43.0 for HTTP proxies, 7.49.0 for SOCKS5 proxies.
Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.