using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.DirectoryServices;
using System.DirectoryServices.AccountManagement;

public class LdapAuthentication
{
    // class variables
    private string _path;
    private string _filterAttribute;

    // default class constructor
    public LdapAuthentication(string _domain, string _username, string _password)
    {
        IsAuthenticated(_domain, _username, _password);
    }

    // grabs the root LDAP path for the current domain in which this program is ran
    void InitializeLdapPath()
    {
        DirectoryEntry de = new DirectoryEntry("LDAP://RootDSE");
        _path = @"LDAP://" + de.Properties["defaultNamingContext"].Value.ToString();
    }

    // public method to test authentication and set our variables
    public bool IsAuthenticated(string domain, string username, string pwd)
    {
        InitializeLdapPath();
        string domainAndUsername = domain + @"\" + username;
        DirectoryEntry entry = new DirectoryEntry(_path, domainAndUsername, pwd);
        try
        {
            // use supplied creds to bind to ad
            // this forces auth to occur
            Object obj = entry.NativeObject;
            DirectorySearcher searcher = new DirectorySearcher(entry);
            searcher.Filter = "(SAMAccountName=" + username + ")";
            searcher.PropertiesToLoad.Add("cn");
            SearchResult r = searcher.FindOne();
            if(r == null)
            {
                return false;
            }
            // update our variables
            _path = r.Path.ToString();
            _filterAttribute = (String)r.Properties["cn"][0].ToString();
        }
        catch (Exception ex)
        {
            throw new Exception("Error authenticating user. " + ex.Message);
        }

        // if everything above runs fine, return true
        return true;
    }
}