Laravel Passport is an easy to use OAuth2 server that was released alongside Laravel 5.3. Mohamed Said wrote an excellent guest post at Laravel News about the grant types used in Passport.

OAuth2 is a security framework that controls access to protected areas of an application, and it’s mainly used to control how different clients consume an API ensuring they have the proper permissions to access the requested resources.

Laravel Passport is a full OAuth2 server implementation; it was built to make it easy to apply authentication over an API for laravel-based web applications.