transfer a URL

-k, --insecure
       (SSL)  This option explicitly allows curl to perform "insecure" SSL connections and transfers. All
       SSL connections are attempted to be made secure by using the CA certificate  bundle  installed  by
       default. This makes all connections considered "insecure" fail unless -k, --insecure is used.

       See this online resource for further details: http://curl.haxx.se/docs/sslcerts.html