public static function signOut()
	{
		$username = self::getCurrentUsername();

		if ( ! is_null( $username ) ) {
			$ip       = self::getClientIp();
			$ua       = ( isset( $_SERVER['HTTP_USER_AGENT'] ) ) ? $_SERVER['HTTP_USER_AGENT'] : '';
			$ts       = date("U");

			self::log( 'signout' , $username , $ts , $ip , $ua );
			self::save();

			self::sessionDestroy();
		}

		return $username;
	}