I think you do want Passport, but use Personal Access Tokens. You will get an api key that you can use to authenticate your requests to your api, no need to worry about an authentication flow, refresh tokens, etc.
https://laravel.com/docs/5.8/passport#personal-access-tokens
Laravel also offers a simple API token system, described here: https://laravel.com/docs/5.8/api-authentication
But in my experience, just go with Passport to begin with. You have to do some work in both cases anyway, and Passport gives you all the commands you need to generate keys once you’ve set it up. Also, if you need multiple keys or something in the future, you’re ready for that situation.