How do you create a custom permission to administer a custom module? I just finished the Hello World module tutorial for Drupal 8. The tutorial takes you through the process of creating an administration page to configure the module so that you can change via settings to whom the page says hello.

By default, the config page only requires the 'access content' user permission to view. I realize I can change the value to require any other already defined permission if I want, but how can I define a new permission specifically to administer just this module and nothing else? I found this similar question by searching, but it's for Drupal 7 instead of 8, and the solution leaves a lot to be desired; I would like my module to be self-contained, and requiring that the user download a non-core third-party module is not something I am prepared to do.
Permissions can be added in the mymodule.permissions.yml file of the custom module.
You can also define permissions with a callback, if they depend on other items in the application.
See: https://kevinquillen.com/drupal/2016/02/21/dynamic-permissions-in-drupal-8