While most password managers and other autofill modules require authentication to validate data entry, Google Autofill has so far been an exception.
As soon as your device is unlocked, Google's autofill module automatically validates the entry of your passwords, bank details, addresses, etc. within forms or login pages.
Authentication by fingerprint or facial recognition
However, things should change very soon. Google will indeed strengthen the security of its autofill system on Android by including the obligation to authenticate to validate data entry.
Depending on the security system built into your mobile device, Google Autofill will soon ask users to authenticate, either by using the fingerprint sensor built into the device or by using the facial recognition module.
Deployment of this more secure system is expected to arrive in the coming weeks on Android smartphones through an update to Google Play services.
Source: Android Police