OAuth 2.0 Authorization State Diagram Template

This state diagram template maps every discrete state and transition in the OAuth 2.0 Authorization Code Grant flow, from the initial unauthenticated state through authorization request, user consent, code exchange, token issuance, and finally an authenticated session. Each node represents a system or user state—such as "Awaiting Authorization," "Code Issued," "Token Active," and "Token Expired"—while the arrows capture the events and conditions that trigger each transition, including redirects, HTTP callbacks, and error responses. Security-sensitive states like token refresh and revocation are also modeled, giving engineers a complete picture of the protocol lifecycle in a single visual reference.

## When to Use This Template

This template is most valuable when onboarding new developers to an OAuth 2.0 integration, conducting security reviews, or designing a new identity provider implementation. Because the Authorization Code Grant is the recommended flow for server-side web applications and involves multiple parties—client, authorization server, and resource server—a state diagram makes the handoffs and failure paths explicit in a way that prose documentation cannot. Teams building single-page applications with PKCE extensions can also adapt this template by adding the code verifier and challenge states, making it a flexible starting point for any variant of the flow.

## Common Mistakes to Avoid

One frequent error is omitting error and timeout states, which leaves the diagram incomplete and misleads reviewers into thinking the happy path is the only path. Always model states like "Authorization Denied," "Invalid Code," and "Token Expired" to reflect real-world behavior. Another mistake is conflating the client state with the authorization server state on the same diagram without clear labeling—use swimlanes or color coding to distinguish which actor owns each state. Finally, avoid drawing transitions without labeling the triggering event and any guard conditions (for example, "redirect with code" or "[code not expired]"), as unlabeled arrows make the diagram ambiguous and reduce its value as documentation.