If you are not familiar with OAuth or OAuth 2.0, it is a standard for authorization. The implementation of OAuth revolves around the usage of tokens sent in HTTP headers. Refer to the OAuth home page for more information at http://oauth.net/.

By following the Enabling RESTful interfaces recipe, you should have the REST UI module added to your Drupal installation using Composer. This can be done with the following command:

cd /path/to/drupal8
composer require drupal/restui