public function assignGroup($username, $add = null, $remove = null, $reason = null)
	{
		// Get the token.
		$token = $this->getToken($username, 'unblock');

		// Build the request path.
		$path = '?action=userrights';

		// Build the request data.
		$data = array(
			'username' => $username,
			'token'    => $token,
			'add'      => $add,
			'remove'   => $remove,
			'reason'   => $reason,
		);

		// Send the request.
		$response = $this->client->post($this->fetchUrl($path), $data);

		return $this->validateResponse($response);
	}