PHP curl request with ssl/tls client certificate

cert-curl.php

<?php
//source: http://www.zedwood.com/article/php-curl-connect-with-ssl-client-certificate
class SecureRequest
{
    private m_publicCertPath; //"/public_cert.pem"
    private m_privateCertPath; //"/private.pem")
    private m_caInfoPAth; //"/etc/ssl/certs/ca-certificates.crt"
    
    public function init($publicCertPath, $privateCertPath, $caInfoPath) {
        $this->m_publicCertPath = $publicCertPAth;
        $this->m_privateCertPath = $privateCertPath;
        $this->m_caInfoPath = $caInfoPath;
    }
    
    public function post($url, $data) {
        return $this->sendRequest("POST", $url, $data);
    }
    
    public function get($url, $data) {
        $queryData = http_build_query($data);
        $urlWithData = $url . '?' . $queryData;
        return $this->sendRequest("GET", $urlWithData, array());
    }
    
    private function sendRequest($method, $url, $data) {
        //TODO: enforce https://-url
        //$data = array('key'=>'value');
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_PORT , 443);
        curl_setopt($ch, CURLOPT_VERBOSE, 0);
        curl_setopt($ch, CURLOPT_HEADER, 0);
        curl_setopt($ch, CURLOPT_SSLCERT, $this->m_publicCertPath);
        curl_setopt($ch, CURLOPT_SSLKEY, $this->m_privateCertPath);
        curl_setopt($ch, CURLOPT_CAINFO, $this->m_caInfoPath);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 1);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
                
        if( strtoupper($method) == "POST" )
        {
            curl_setopt($ch, CURLOPT_POST, 1);
            curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($data));
        }

        $response = curl_exec($ch);
        //$info =curl_errno($ch)>0 ? array("curl_error_".curl_errno($ch)=>curl_error($ch)) : curl_getinfo($ch);
        //print_r($info);
        curl_close($ch);
        return $response;
    }
}
?>

Ok, in your case you are the client.
But the above code uses certificate authentication.

If you don't need certificate authentication, you must comment out lines 33 to 36 or just search the web how to use php with curl. There should be enough pretty straight forward tutorials about this topic.

I'm having some issues with my case. the API owner sent me a public certificate "Certificate.cer" file. how do I sent it with my request as I don't have private keys and ".pem" file ?