const AthomCloudAPI = require('homey-api/lib/AthomCloudAPI');
​
// Create a Cloud API instance
const cloudApi = new AthomCloudAPI({
  clientId: '...',
  clientSecret: '...',
});
​
// Get the logged in user
const user = await cloudApi.getAuthenticatedUser();
​
// Get the first Homey of the logged in user
const homeyApi = await user.getFirstHomey();
​
// Create a session on this Homey
const homey = await homey.authenticate();
​
// Loop all devices
const devices = await homey.devices.getDevices();
for(const device of Object.values(devices)) {
  // Turn device on
  await device.setCapabilityValue('onoff', true); 
}