CURLOPT_PROXY_KEYPASSWD

CURLOPT_PROXY_KEYPASSWD is one of the accepted parameters for curl_setopt parameter #2.

CURLOPT_PROXY_KEYPASSWD — Set the string be used as the password required to use the CURLOPT_PROXY_SSLKEY private key. You never needed a passphrase to load a certificate but you need one to load your private key. This option is for connecting to an HTTPS proxy, not an HTTPS server. Available as of PHP 7.3.0 and cURL 7.52.0

CURLOPT_PROXY_KEYPASSWD = 10258;