server {
    listen 443 ssl;
    server_name a.com;

    ssl_certificate /path/to/certs/a.com.pem;
    ssl_certificate_key /path/to/certs/a.com.key;
    ssl_session_cache shared:SSL:1m;
    ssl_session_timeout  5m;
    ssl_ciphers ECDHE-RSA-AES128-GCM-SHA256:ECDHE:ECDH:AES:HIGH:!NULL:!aNULL:!MD5:!ADH:!RC4;
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
    ssl_prefer_server_ciphers on;
}

多域名多 SSL 证书配置参考：多域名多 SSL 证书配置