public static function authenticate() {
		$credentials = array(
			'calendar_guid' => (int) get_input('guid'),
			'user_guid' => (int) get_input('u'),
			'token' => get_input('t'),
		);

		$pam = new ElggPAM(self::POLICY);
		$authenticated = $pam->authenticate($credentials);
		if (!$authenticated) {
			throw new LoginException($pam->getFailureMessage());
		} else {
			$user = get_entity($credentials['user_guid']);
			login($user);
		}
		return $authenticated;
	}