LoginView.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"
             x:Class="LoginViewSample.Core.Views.LoginPage">
    <ContentPage.Content>
        <Grid Margin="16">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="*"/>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>
            <StackLayout Grid.Row="0">
                <Label Text="Please enter your credentials" />
                <Entry Text="{Binding Username}"
                       Placeholder="Username" />
                <Entry Text="{Binding Password}"
                       Placeholder="Password"
                       IsPassword="True" />
                <Label Text="Invalid credentials entered" 
                       IsVisible="{Binding AreCredentialsInvalid}" 
                       TextColor="Red" />
            </StackLayout>
            <Button Grid.Row="2" Text="Authenticate" Command="{Binding AuthenticateCommand}" />
        </Grid>
    </ContentPage.Content>
</ContentPage>