CURLOPT_PROXY_SSLCERT

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

CURLOPT_PROXY_SSLCERT — A string with the file name of the client certificate used to connect to the HTTPS proxy. The default format is P12 on Secure Transport and PEM on other engines, and can be changed with CURLOPT_PROXY_SSLCERTTYPE. With NSS or Secure Transport, this can also be the nickname of the certificate used for authentication as it is named in the security database. If a file from the current directory is to be used, it must be prefixed with ./ in order to avoid confusion with a nickname. Available as of PHP 7.3.0 and cURL 7.52.0.

CURLOPT_PROXY_SSLCERT = 10254;