Biometrics are not it. Anyone can forcefully grab your finger and place it onto your phone screen. They can hold the phone up to your face.

Secure keys or passwords (actual authority) are only vulnerable to rubber-hose cryptanalysis, but you can use plausibly deniable measures to reduce the risk.

Both are bits of data stored in the body (including mind and pockets) that suggest the owner is giving consent.

They both have flaws, but what are the alternatives?

The mind provides authority.

Use both!

But don't mix them up.

I think a better solution for authentication is a combination of a cryptographic key or seed and a passphrase held in the mind. Keys could be provided by an NFC ring, which should be more difficult to lose or have stolen than a phone.