The Add-on for Cloudflare data app is best installed on a heavy forwarder, as it is managed using the web interface.
On a heavy forwarder, install the app using Apps->"Manage Apps"->"Install app from file", then upload the file.
You can then navigate to the app using the Apps dropdown in the upper-left, then selecting the app. On the upper left you can go to Configuration, then Add-on Settings, then enter your X-auth email and key for cloudflare. Then you can go to the Inputs menu on the upper left and press "Create New Input" (in the upper right).
Then you can create inputs for various data types, specifying the index and interval of collecting the logs from the Cloudflare API.
Once this is done, and if your heavy forwarder can connect to cloudflare, then it should start indexing logs in sourcetypes beginning with cloudflare:*
e.g.
index=<yourindex> sourcetype=cloudflare:*
