Before we understand OIDC, let's make sure we understand authentication and authorization. Authentication verifies that the user is who they say they are. In our app, the user will enter their email and password to prove who they are. Authorization decides whether a user has permission to access a resource. In our app, some of the REST API endpoints, such as posting a question, will eventually be protected by authorization checks.
OIDC is an industry-standard way of handling both authentication and authorization as well as other user-related operations. This works well for a wide variety of architectures including single-page applications (SPAs) such as ours where there is a JavaScript client and a server-side REST API that need to be secured.
The following diagram shows the high-level flow of a user of our app being authenticated and then gaining access...
