FirebaseUIInit.cs

// Initialize FirebaseUI during your application startup (e.g. App.xaml.cs)
FirebaseUI.Initialize(new FirebaseUIConfig
{
    ApiKey = "<API KEY>",
    AuthDomain = "<DOMAIN>.firebaseapp.com",
    Providers = new FirebaseAuthProvider[]
    {
        new GoogleProvider().AddScopes("email"),
        new EmailProvider()
        // and others
    },
    PrivacyPolicyUrl = "<PP URL>",
    TermsOfServiceUrl = "<TOS URL>",
    IsAnonymousAllowed = true,
    UserRepository = new FileUserRepository("FirebaseSample") // persist data into %AppData%\FirebaseSample
});