How does Google Home app Automatically fetch WIFI password?

[AC Question]

I am looking to add this auto fetch WIFI password feature to an app. I have been looking through the API and I can not find a reference to this. I can only find it in the setup instructions for connecting to chromecast in step 12 of "Set up Chromecast" for Android. (link was marked as spam)

How is this feature being implemented? Am I overlooking something in the API?