How to use curl with RTC rest API to get project history ?

  Hi All:

 I want to extract data from RTC rest API.

   I am sure the url link is valid as I can open it after I input my id and password. But I can not get anything by the following command.could anyone help on this?thanks in advance.

curl -k -u "myibmid":"password" -o tmp4.xml https://XXXXX.XXXX.XXXX.XXXX.com:9443/ccm/process/project-areas/_sDggwO0WXXXXXXXX/history 

If I remove -k from the command above, it will say as below:

curl: (60) Peer certificate cannot be authenticated with known CA certificates
More details here: http://curl.haxx.se/docs/sslcerts.html

curl performs SSL certificate verification by default, using a "bundle"
 of Certificate Authority (CA) public keys (CA certs). If the default
 bundle file isn't adequate, you can specify an alternate file
 using the --cacert option.
If this HTTPS server uses a certificate signed by a CA represented in
 the bundle, the certificate verification probably failed due to a
 problem with the certificate (it might be expired, or the name might
 not match the domain name in the URL).
If you'd like to turn off curl's verification of the certificate, use
 the -k (or --insecure) option.