One or two inputs on which to evaluate PRF. Not all authenticators support evaluating the PRFs during credential creation so outputs may, or may not, be provided. If not, then an assertion is needed in order to obtain the outputs.
OptionalevalA record mapping base64url encoded credential IDs to PRF inputs to evaluate for that credential. Only applicable during assertions when allowCredentials is not empty.
PRF extension inputs
See
https://w3c.github.io/webauthn/#dictdef-authenticationextensionsprfinputs