LdapAuthentication.cs

using System.DirectoryServices;
using System.DirectoryServices.Protocols;
using System.Net;

bool ValidateUser(string username, string password)
{
    bool authorized = false;
    
    using(LdapConnection connection = new LdapConnection("192.168.0.5"))
    {
        connection.AuthType = AuthType.Basic;
        connection.AutoBind = false;
        connection.Timeout = new TimeSpan(0, 0, 10);
        connection.SessionOptions.ProtocolVersion = 3;
            
        try 
        {
            var credential = new NetworkCredential(string.Format("uid={0},ou=Users,dc=domain,dc=com,dc=br", username), password);
            connection.Bind(credential);
            authorized = true;
        } 
        catch (LdapException)
        {
            // authentication failed
        }
    }
    
    return authorized;
}