How Auto start apps are able to start after reboot?

Many OEMs have restrictions which do not allow an application to run after boot complete. For this, we need to give autostart permission to that app. Then how does apps like Autostart, startup manager are able to run right after boot without having any permissions? Autostart is developed by a small team and is not as popular as whatsapp, facebook and others that it can be whitelisted by the OEM. Any inputs will be helpful. Edit1: I am aware of broadcast receiver but even after using them user needs to manually set autostart permission for my application to be able to run the application in background after BOOT_COMPLETE. However this is not the case for autostart apps. Thanks.