Configuring automatic login shouldn't be difficult. Here are instructions on Ubuntu (should work on any GNOME system), and here's how to do it with pretty much any KDE system. This is a feature of desktop managers (like gdm or sddm), not desktop environments (like GNOME or KDE), so if neither works for you, you're probably using a different one. If that's the case, reply with your distro and as much info as you can provide.

That said, what exactly is the problem you're trying to solve? It's usually a lot easier to login remotely using SSH instead of remote desktop, and then use console commands to do whatever you need. To login with SSH:

ssh <user>@<IP address>

So if your username is tux and your IP is 1.2.3.4:

ssh tux@1.2.3.4

And then if you want to reboot:

sudo reboot

And if you want to shutdown:

sudo shutdown -h now

I use an app on my phone to login, so I can get it done while sitting on the toilet in like 10s (I use it to unlock my computer so my kids can use it). If you're accessing from your computer and just need to run a single command, provide it after the command in quotes (note, sudo commands won't prompt for a password and will just fail).