OAuth, a complex but essential protocol for secure authorization, allows third-party applications to access user data without sharing passwords. This guide emphasizes practical understanding, focusing on the OAuth "Authorization Code Flow," which enables scoped access for apps like the fictional "Content Planner" to post on social media platforms on behalf of users without accessing their login credentials. Key security measures, such as PKCE and state parameters, are discussed to prevent unauthorized access and ensure secure token exchanges. The guide also addresses common OAuth questions, such as token expiration and refresh, opaque versus JWT tokens, and the potential risks and benefits of dynamic client registration. Additionally, it touches on OpenID Connect (OIDC), which enhances OAuth by providing user identity information. For developers using Clerk, the platform offers built-in support for OAuth implementations, including dynamic client registration and robust security features.