If you want to connect to a server which requires that you identify yourself with a certificate, use following code. Your certificate and servers certificate are signed by an authority whose certificate is in ca.ctr. 

<?php 
curl_setopt($ch, CURLOPT_VERBOSE, ‘1‘); 　　　　//启用时会汇报所有的信息，存放在STDERR或指定的 CURLOPT_STDERR 中。
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, ‘2‘); 　　//2 检查公用名是否存在，并且是否与提供的主机名匹配。
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, ‘1‘); 　　//cURL从服务端进行验证
curl_setopt($ch, CURLOPT_CAINFO,  getcwd().‘/cert/ca.crt‘); 
curl_setopt($ch, CURLOPT_SSLCERT, getcwd().‘/cert/mycert.pem‘); 
curl_setopt($ch, CURLOPT_SSLCERTPASSWD, ‘password‘); 
?> 

If your original certificate is in .pfx format, you have to convert it to .pem using following commands 
# openssl pkcs12 -in mycert.pfx -out mycert.key 
# openssl rsa -in mycert.key -out mycert.pem 
# openssl x509 -in mycert.key >> mycert.pem