Example of how to implement Biometric Authentication in Xamarin.Forms applications - http://julianocustodio.com/autenticacao-biometrica

MainPage.xaml

<?xml version="1.0" encoding="utf-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
             xmlns:local="clr-namespace:BiometricDemo" 
             x:Class="BiometricDemo.MainPage" Padding="10">
    <StackLayout VerticalOptions="Center">
        <Button Clicked="Autenticar" Text="Autenticar" BackgroundColor="#F3F3F3"/>
        <Label x:Name="Resultado" Text="" HorizontalTextAlignment="Center"/>
    </StackLayout>
</ContentPage>