Protocol for retrieving common fields from public key credential structs.

This protocol is used when a list of credentials is passed to WebauthnComponents.AuthenticationComponent.update/2 to extract the fields required to validate a pending authentication request.

For convenience, a default implementation is provided to pattern match on :id and :public_key fields from any struct or map.

Custom Implementation

If your public key credential schema/struct uses alternate field names, you may define a custom implementation. The following example schema uses a slightly different naming convention for its fields, so a custom implementation is defined:

defmodule MyApp.Identity.PublicKeyCredential do
  use Ecto.Schema
  alias MyApp.Identity.User

  @primary_key {:key_id, :binary, autogenerate: false}
  schema "public_key_credentials" do
    field :pub_key, WebauthnComponents.CoseKey
    field :label, :string, default: "Default"
    belongs_to :user, User
    timestamps()
  end

  defimpl WebauthnComponents.CredentialProtocol do
    def id(%{key_id: key_id}), do: key_id
    def public_key(%{pub_key: pub_key}), do: pub_key
  end
end