Laravel 5.6 has a native API authentication middleware as an alternative to Passport (https://laravel.com/docs/5.6/passport). If you are not running an up-to-date version of PHP on your servers however, you are going to have some difficulties using Password (as I learned the hard way). After doing some digging I ran across an article for versions 5.2 and 5.3 (see link below) which I found still applicable.
Create field in users table
You will need to run
php artisan migrateafter you make the change.
Add Guard and Provider in
Add Middleware to controllers:
In your controller construct function add
$this->middleware( 'auth:token' );
There are some security caveats with this method and I would recommend using Passport, but if you need something simple you do have another option.