for secure pins, can we use Touch ID instead of a four digit pin?
I don't believe this is possible. There is no Web API to access Touch ID.
If such API appears, I would be curious to investigate if it could be used for AT.
I presume you are referring to iOS Touch ID? (Though Android has standards for hardware biometric authentication too).
I can only paste this as a Feature Request to see if it is popular. PIN entry is compatible with everything, so we don't have to mess with hardware access services. So we would want to see substantial interest.
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