Laravel API Authentication

I am building an API using Laravel which will be used by both my Mobile and Web Applications. I am confused regarding authentication.

Basically the web application will be used by users both in logged in state and visitor state.

How would authentication work in that case? If the API uses username/password to authenticate a user what about visitors?

Also, how do I make sure its the webapp and mobile app thats making a request to the API? How do I ensure that someone doesn't programatically doesn't access the API and its only my apps that can request access to data?

via Chebli Mohamed