The Arduino IoT Cloud also provides other methods of interaction

In the press release (Announcing the Arduino IoT Cloud Public Beta) there is stated:

The Arduino IoT Cloud also provides other methods of interaction, including HTTP REST API, MQTT, Command-Line Tools, Javascript, and Websockets.

Any documentation describing these?
Ideally I want IFTTT or NodeRed linked to the Arduino IoT Cloud. That would make the Arduino interactively connected to the world :o

The "webhook" functionality that you find the IOT Cloud now can communicate with IFTTT, Zapier and Google. The list of domains is limited to avoid abuse.

After that we'll enable a version that can talk to any domain. Finally we'll enable the API which will allow you to connect to anything. we plan to release a node-red module when that feature is enabled.

What you see now is the MVP, it only shows 1% of the features we have in the roadmap. there will be regular releases so expect new features to appear on a regular basis (we're currently deciding how frequently to release stuff so that people can expect regular release cycles)

I tried using a ifttt webhooks, and got this error :
You can't create the webhook on domain maker.ifttt.com

Edit:
It accepts it when you change the webhook from
IFTTT Maker Webhooks to https://ifttt.com/use/{key}
But this won't works as the webhook is at maker.ifttt.com not ifttt.com.

madnerd has created a dedicated thread for the ifttt webhooks topic: