Curl uses SSL Certificate Verification by default.
So When you try to use curl, you might run into this error

curl: (60) SSL certificate problem, verify that the CA cert is OK. Details:
error:14090086:SSL routines:SSL3GETSERVER_CERTIFICATE:certificate verify failed
More details here: http://curl.haxx.se/docs/sslcerts.html

To Skip the default Curl SSL Certificate Verification use curl with -k option as

curl -k URL