The options "--ntlm --negotiate" and "-u" are required!
1. By specifying the user name and password
curl --ntlm --negotiate -u "DOMAIN\NAME:PASSWORD" "http://combitreportserver/api/....."
2. Use user account of the current process (colon instead of user name & password)
curl --ntlm --negotiate -u : "http://combitreportserver/api/....."