Custom api token validation

Hi to all! I used Laravel years ago (version 5.4)and now I'm back on a project.. so I'm a bit rusty :)

In my application I have an API that is called with a Bearer token, I don't have methods for /login, /register etc. I just have to validate the token with a custom authentication service.

So, the user will directly call an endpoint with a Bearer token and I have to validate it.

How i can simply validate token, without use the "standard" flow that provide the /login etc?

I know that is a very generic question, but right now i dont have any working examples on how i'm trying to implement this :(