I have two virtual hosts and SSL is configured on both of these servers. Both these servers have their own .key (private key) and .crt (public key) files.

I need to send a curl request from PHP script on server 1 to PHP Script on server 2 and I need to use HTTPS for this curl request.

The public key (.crt file) is shared between these two servers. When I am sending curl request from server 1 to server 2, I am getting the error below:
SSL certificate problem, verify that the CA cert is OK. Details:
error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
I tried to send the Server 2 public key in the curl request using the code below:

PHP Code:
curl_setopt$curlCURLOPT_SSLCERT'/opt/certificates/server2.crt' ); 
and got the error below:
unable to set private key file: '/opt/sage/certificates/AS/aspchart-server.crt' type PEM
Sometimes I may need to send client certificate also. How can I send Curl HTTPS request in PHP Script?

Thanks in advance.