https://components.xamarin.com/gettingstarted/loginscreen to new Activity

Activity1.cs

using System;

using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;

using LoginScreen;

namespace LoginScreen.Android.Sample
{
	[Activity (Label = "LoginScreen.Android.Sample", MainLauncher = true)]
	public class Activity1 : Activity
	{
		protected override void OnCreate(Bundle bundle)
		{
			base.OnCreate(bundle);

			SetContentView(Resource.Layout.Main);

			FindViewById<Button>(Resource.Id.loginButton).Click += (sender, e) => LoginScreenControl<TestCredentialsProvider>.Activate(this);
		}
	}
}

Activity2.cs

using System;

using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;

using LoginScreen;

namespace LoginScreen.Android.Sample
{
	[Activity (Label = "Activity2")]
	public class Activity2 : Activity
	{
		protected override void OnCreate(Bundle bundle)
		{
			base.OnCreate(bundle);

			SetContentView(Resource.Layout.Main);

            Button b = FindViewById<Button>(Resource.Id.loginButton);
            b.Text = "Activity 2 Button";
		}
	}
}

CustomApplication.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;

namespace LoginScreen.Android.Sample
{
    [Application]
    public class CustomApplication : Application
    {
        public CustomApplication(IntPtr handle, JniHandleOwnership ownerShip)
            : base(handle, ownerShip)
        {
        }
        public override void OnCreate()
        {
            base.OnCreate();
        }

        public static Context GetAppContext()
        {
            return CustomApplication.Context;
        }

        public static void ChangeActivity()
        {
            Intent i = new Intent(Context, typeof(Activity2));
            i.AddFlags(ActivityFlags.NewTask);
            Context.StartActivity(i);
        }
    }
}

Main.axml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="#FFFFFF">
    <Button
        android:id="@+id/loginButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:textColor="#000000"
        android:text="Login" />
</RelativeLayout>

TestCredentialsProvider.cs

using System;
using System.Timers;

using LoginScreen;

namespace LoginScreen.Android.Sample
{
	public class TestCredentialsProvider : ICredentialsProvider
	{
		readonly Random rnd = new Random ();

		public bool NeedLoginAfterRegistration {
			get { return false; }
		}

		public bool ShowPasswordResetLink {
			get { return true; }
		}

		public bool ShowRegistration {
			get { return true; }
		}

		public void Login (string userName, string password, Action successCallback, Action<LoginScreenFaultDetails> failCallback)
		{
			DelayInvoke (EquiprobableSelect (successCallback, () => failCallback (new LoginScreenFaultDetails { CommonErrorMessage = "Something wrong happened." })));

            CustomApplication.ChangeActivity();
		}

		public void Register (string email, string userName, string password, Action successCallback, Action<LoginScreenFaultDetails> failCallback)
		{
			DelayInvoke (() => {
				if (password.Length < 4) {
					failCallback (new LoginScreenFaultDetails { PasswordErrorMessage = "Password must be at least 4 chars." });
				} else {
					successCallback ();
				}
			});
		}

		public void ResetPassword (string email, Action successCallback, Action<LoginScreenFaultDetails> failCallback)
		{
			DelayInvoke (EquiprobableSelect (successCallback, () => failCallback (new LoginScreenFaultDetails { CommonErrorMessage = "Something wrong happened." })));
		}

		private void DelayInvoke (Action operation)
		{
			Timer timer = new Timer ();
			timer.AutoReset = false;
			timer.Interval = 3000;
			timer.Elapsed += (object sender, ElapsedEventArgs e) => operation.Invoke ();
			timer.Start ();
		}

		private T EquiprobableSelect<T> (T first, T second)
		{
			return rnd.Next (100) < 50 ? first : second;
		}
	}
}