public Authorization Authenticate( string challenge,WebRequest request,ICredentials credentials)
{
    try
    {
        string message;
        // Check if Challenge string was raised by a site which requires 'CloneBasic' authentication.
        if ((challenge == null) || (!challenge.StartsWith("CloneBasic")))
            return null; 
        NetworkCredential myCredentials;
        if (credentials is CredentialCache)
        {
            myCredentials = credentials.GetCredential(request.RequestUri,"CloneBasic");
            if (myCredentials == null)
                return null;
        }
        else
        {
            myCredentials = (NetworkCredential)credentials;
        }
        // Message encryption scheme : 
        //   a)Concatenate username and password seperated by space;
        //   b)Apply ASCII encoding to obtain a stream of bytes;
        //   c)Apply Base64 Encoding to this array of bytes to obtain our encoded authorization message.

        message = myCredentials.UserName + " " + myCredentials.Password;
        // Apply AsciiEncoding to 'message' string to obtain it as an array of bytes.
        Encoding ascii = Encoding.ASCII;
        byte[] byteArray = new byte[ascii.GetByteCount(message)];
        byteArray = ascii.GetBytes(message);

        // Performing Base64 transformation.
        message = Convert.ToBase64String(byteArray);
        Authorization myAuthorization = new Authorization("CloneBasic " + message,true);
        string[] protectionRealm = new string[]{request.RequestUri.AbsolutePath};
        myAuthorization.ProtectionRealm = protectionRealm;

        return myAuthorization;
    }
    catch(Exception e)
    {
        Console.WriteLine("The following exception was raised in Authenticate method:{0}",e.Message);
        return null;
    }
  }