Idea: Module Argument to force PIN or UV

[My1]

Is your feature request related to a problem?

the pinverification is specifically about PINs and userverification as written is the comments is specifically about on-device UV (such as fingerprints).

Users with mixed setups (e.g. a fingerprint authenticator for convenience and a cheaper non-bio model as backup) would be required to not enable either of these if they want to use both seamlessly as the options from the way they are written would kinda create issues with each other if both are set.

the PIN only key would likely not work at all due to the UV requirement, and not even sure what the UV-enabled key would do (and that doesnt even include the keys of a UV-enabled key that supports PIN but the UV tries are exhausted.

Describe the solution that you'd like

an option that instead of forcing either UV or PIN, that basically tries UV if available, otherwise use the PIN

Describe the alternatives that you've considered

honestly the only super weird thing that could work is having multiple configs at the same time which would be kinda cumbersome to keep track of

Additional context

I cant really help with the programming but I can sure help testing

[LDVG]

Yes, there's certainly room for improvement in ergonomics here. In the meantime, have you considered handling this directly in the PAM stack?

pam-u2f/README

Lines 369 to 380 in b5846bb

	==== Passwordless Authentication using Biometrics
	Similar to the previous configuration but capable of built-in user
	verification, e.g. fingerprint matching using the YubiKey Bio. This example
	falls back to using PIN verification if the fingerprint does not match or is
	otherwise blocked.
	----
	auth sufficient pam_u2f.so authfile=/etc/u2f_mappings cue pinverification=0 userverification=1
	auth sufficient pam_u2f.so authfile=/etc/u2f_mappings cue pinverification=1 userverification=0
	# More fallback modules go below this line (e.g. password authentication).
	----

[My1]

honestly I havent seen that section as I set it up half an eternity ago and iirc used another tutorial and therefore didnt look beyond the table, but I would have thought that something like this might be a bit chaotic and need multiple interactions with some potentially causing errors and stuff