Private Cloud Collection

In order to secure access to a Cloud Collection content you need to make it private.
That setting is available under Cloud Collection 'Advanced settings' (Under Connect tab):

Under Advanced Settings set 'Public Feed' to No 

To Access a Private Cloud Collection you need to send the Private Key along with the Request.

The process of Setting a Private Key is described in  'Authorize Write Access to a Cloud Collection API Key' 

Once they key has been created, you MUST pass that key along your request when access that Cloud Collection.

When using a Private Collection the feed will be automatically updated to send the key: Using Private Feeds