CURLOPT_PROXY_TLSAUTH_USERNAME

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

CURLOPT_PROXY_TLSAUTH_USERNAME — The username to use for the HTTPS proxy TLS authentication method specified with the CURLOPT_PROXY_TLSAUTH_TYPE option. Requires that the CURLOPT_PROXY_TLSAUTH_PASSWORD option to also be set. Available as of PHP 7.3.0 and cURL 7.52.0.

CURLOPT_PROXY_TLSAUTH_USERNAME = 10251;