Understanding OAuth 2.0 and OpenID Connect

Previously, we learned how to implement authentication and authorization using built-in Identity APIs in ASP.NET Core. However, you may encounter some terms such as OAuth 2.0 and OpenID Connect when you work on a real project. It would be helpful to understand what they are and how to use them in ASP.NET Core. It is worth authoring a full book on OAuth 2.0 and OpenID Connect. In this section, we will introduce some basic concepts surrounding OAuth 2.0 and OpenID Connect, as well as some third-party authentication and authorization providers.

What is OAuth 2.0?

Let’s start with a real example. When you use LinkedIn, you may see a window that prompts you to sync your contacts from Outlook, Gmail, Yahoo, or other email services. This is because LinkedIn would like to know your contacts so that it can recommend you to invite your friends to join LinkedIn or to connect with them. This is a typical example where OAuth 2.0 is used:

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