C#

[DirectoryObjectClass("person")]
[DirectoryRdnPrefix("CN")]

public class UserPrincipalExtension : UserPrincipal
{
    // Implement the constructor using the base class constructor.
    public UserPrincipalExtension(PrincipalContext context, string userName) : base(context) { }

    // Implement the constructor with initialization parameters.
    public UserPrincipalExtension(PrincipalContext context,
                     string samAccountName,
                     string password,
                     bool enabled)
        : base(context,
               samAccountName,
               password,
               enabled)
    {
    }

    UserPrincipalExSearchFilter searchFilter;

    new public UserPrincipalExSearchFilter AdvancedSearchFilter
    {
        get
        {
            if (null == searchFilter)
                searchFilter = new UserPrincipalExSearchFilter(this);

            return searchFilter;
        }
    }

    [DirectoryProperty("extensionAttribute1")]
    public string extensionAttribute1
    {
        get
        {
            if (ExtensionGet("extensionAttribute1").Length != 1)
                return null;

            return (string)ExtensionGet("extensionAttribute1")[0];

        }
        set { this.ExtensionSet("extensionAttribute1", value); }
    }

    // Implement the overloaded search method FindByIdentity
    public static new UserPrincipalExtension FindByIdentity(PrincipalContext context,
                                                   string identityValue)
    {
        return (UserPrincipalExtension)FindByIdentityWithType(context,
                                                     typeof(UserPrincipalExtension),
                                                     identityValue);
    }

    // Implement the overloaded search method FindByIdentity
    public static new UserPrincipalExtension FindByIdentity(PrincipalContext context,
                                                   IdentityType identityType,
                                                   string identityValue)
    {
        return (UserPrincipalExtension)FindByIdentityWithType(context,
                                                     typeof(UserPrincipalExtension),
                                                     identityType,
                                                     identityValue);
    }
}

public class UserPrincipalExSearchFilter : AdvancedFilters
{
    public UserPrincipalExSearchFilter(Principal p) : base(p) { }
}

public static bool DoesUserExist(string usr)
{
    string methodName = "DoesUserExist: ";
    bool result = false;
    PrincipalContext context = null;
    UserPrincipalExtension user = null;

    try
    {
        context = new PrincipalContext(ContextType.Domain, "MYDOM.LOCAL");


        user = UserPrincipalExtension.FindByIdentity(context, usr);
        if ((user != null) && (user.extensionAttribute1 != null))
        {
            // user id present in AD
            log(methodName, "User does exist. UserID=" + usr + "extension=" + user.extensionAttribute1);
            result = true;
        }
        else
        {
            log(methodName, "User does NOT exist.");
            // User does not exist in AD
        }

    }
    catch (Exception ex)
    {
        log(methodName, "Exception while trying to query Active Directory. " + ex.StackTrace);
        throw ex;
    }
    finally
    {

        // dispose of objects
        user.Dispose();
        context.Dispose();
    }

    return result;
}

public interface IMyInterface
{

string myInterfaceProp{ get; }

}

public class MyClass :IMyInterface
{
public string myInterfaceProp
{
get { return "some value"; }
}

}

public class UserClass
{
MyClass objMyClass =new MyClass ();
objMyClass.
}

How to hide the myInterfaceProp in the userclass when the "MyClass " instance is accessed? .

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private int Test()
        {
            System.Diagnostics.Debug.WriteLine("IN");
            System.Threading.Thread.Sleep(5000);
            System.Diagnostics.Debug.WriteLine("OUT");
            return 17;
        }

        private async Task<int> TestAsync()
        {
            return await Task.Run(() =>
            {
                return Test();
            });
        }

        private void button1_Click(object sender, EventArgs e)
        {
            System.Diagnostics.Debug.WriteLine("BEFORE");
            int a = TestAsync().Result;
            System.Diagnostics.Debug.WriteLine("AFTER");
        }
    }
}

System.IdentityModel.Tokens.SecurityTokenValidationException: The service does not allow you to log on anonymously.

public static string Authenticate(string username, string password)
{
    DomainControllerClient dc = null;

    try
    {
        dc = new DomainControllerClient();
        dc.Open();

        bool success = dc.Authenticate(username, password);
        if (success)
            return "OK";
        else
            return "FAIL";
    }
    catch (Exception ex)
    {
        return ex.ToString();
    }
    finally
    {
        if (dc.State == CommunicationState.Opened)
            dc.Close();
        else if (dc.State == CommunicationState.Faulted)
            dc.Abort();

        dc = null;
    }
}