<?php
public function hasValidCert()
    {
        if (!isset($_SERVER['SSL_CLIENT_M_SERIAL'])
            || !isset($_SERVER['SSL_CLIENT_V_END'])
            || !isset($_SERVER['SSL_CLIENT_VERIFY'])
            || $_SERVER['SSL_CLIENT_VERIFY'] !== 'SUCCESS'
            || !isset($_SERVER['SSL_CLIENT_I_DN'])
        ) {
            return false;
        }

        if ($_SERVER['SSL_CLIENT_V_REMAIN'] <= 0) {
            return false;
        }

        return true;
    }