PasswordProtectedKeyCredentialToRegister

A key pair whose private half the client encrypted with a password of their own. The encrypted
half has to be registered with it - the client cannot sign later without it, and only the client
can produce it.

{
    "kind": "passwordProtectedKey",
    "credentialId": "string",
    "clientData": "string",
    "attestationData": "string",
    "encryptedPrivateKey": "string"
}