FIDO2 touch and fingerprint notification

When the YubiKey is attempting to perform "User Verification" (UV), the end user must verify their fingerprint on the YubiKey's fingerprint reader (this applies to the YubiKey Bio series only).

In addition, some operations, such as MakeCredential or GetAssertion, will not complete until the user touches the contact. For example, a YubiKey will begin an operation, but at some point will stop processing until the contact has been touched. Once touched, it will finish the operation.

In those situations, you will likely want to notify the user that they need to verify their fingerprint or touch the contact. But when exactly do you make that notification?

The SDK will call the KeyCollector at the moment fingerprint or touch is needed. Once it receives that call, the KeyCollector can notify the user.

Normally, the KeyCollector is used to collect something from the user such as a PIN, key, or some other secret value. However, with fingerprint or touch, there is nothing to collect from the user and your application does not need to return anything to the SDK. It is necessary only to notify the user to perform some task.

The KeyCollector and touch article in the User's Manual "SDK programming guide" explains how the process of touch notification works, describes requirements of your KeyCollector, and provides rudimentary samples.