How does Rachio3 receive my WiFi password?

I setup Rachio3 from iPhone. I selected the WiFi SSID of the network to connect to in the app and the Rachio3 controller was able to connect. How does it receive my WiFi password? Is this shared anywhere? I read that an earlier controller uses the BlinkUp technology (BlinkUp sends SSID and password by flashing phone screen and using photosensor on the controller) but this isn’t the case with Rachio3.

@bayarea_user Each controller has an MFI chip produced by Apple that allows us to use their Wireless Accessory Configuration (WAC) process. This process allows us to securely transmit WiFi credentials.