Hello there, I’ve already set a L2TP IpSec VPN at home. Not really super-safe, but built-in iOS and Android. So that, no OpenVPN or WireGuard clients are needed until now.
Assuming I’m trusting my local GL.iNet wi-fi, or lan cable, is there any chance to configure the router as a VPN client connecting home?
VPN client should connect by wan, so I mean ethernet/tethering/usb-key/wifi-extender
UPDATED NOTE: I don’t really trust 3rd parties VPN providers, and installing apps either.
I am sorry to say that L2TP with IPSec is difficult and we do not have a guide to set up on the router.
Thanks @alzhao for your fast reply, I wondered if I can install some sort of OpenWRT plugin as extension, or doing some sort of configuration by entering the ssh console 
You can check here:
Thank you @Johnex this is the documentation useful when you decide to install a L2TP/IPSec server inside your router.
My concern is about the data flowing between the GL.iNet router and the home VPN server.
I wanted to configure my ARM300M as a client, then connect my local devices to it and finally jump inside the internet.
The cost of replacing your server to openvpn or wireguard may be lower than setting up ipsec on the router.
I agree with Alfie. IPsec is an old protocol, slightly faster than OpenVPN but not much, orders of magnitude slower than Wireguard. You are better off replacing your setup with a server that runs Wireguard, and have Wireguard on your AR300m.
Yes, indeed. In the mean time I’ve discovered you can “simply” configure a raspberry with pihole and pivpn.
PiVPN lets you configure OpenVPN or Wireguard as options. I’m stuck in the Wireguard configuration at the moment. I expect I can also connect my ARM300M once fully configured.
The wrong side is you need an application in every device you try to connect, but that’s well embeded inside the mobile operating system (both of them recognize a system vpn) but traffic is tuneled inside the app.
The good part is both kinds of VPN are safer encrypted. Wireguard is expected to be lighter, also.