1) Something you know (password)
2) Something you have (key)
3) Something you are (biometrics)
What this is looking like is only 'something you know' is legally protected. A 'something you have' can be forcibly taken and used to authenticate (a key & a lock). Biometrics are new in mainstream usage.
What it looks like is courts are determining the 'something you are' can be forcibly taken and used as authentication.