Backend concept

OAuth Authorization Code Flow

Authorization Code, PKCE, state, redirect URI validation, and secure token exchange.

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Key takeaway

Authorization Code, PKCE, state, redirect URI validation, and secure token exchange. Start with the related games below when you want to turn the definition into practice.

Why this matters

Small protocol mistakes can leak authorization codes, enable login CSRF, or bind tokens to the wrong client.

How to practice

Validate each browser and back-channel transition, including the values that must remain correlated.

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Learning objectives

Bind callbacks with state.
Preserve the PKCE verifier.
Keep long-lived credentials out of browser JavaScript.
Separate authentication failures from authorization failures.
Recognize token expiration, missing scopes, CSRF risk, and session fixation risk.
Apply object-level authorization instead of trusting a valid token alone.

Common mistakes to avoid

Accepting mismatched state.
Generating a new PKCE verifier after redirect.
Exposing refresh tokens to browser storage.
Treating a valid JWT signature as permission for every object or action.
Returning 401 for authenticated users who lack scope or ownership.
Ignoring CSRF on cookie-authenticated write endpoints.

Games for OAuth Authorization Code Flow

Start with the first game, then use local review history to revisit missed decisions.

Auth Advanced

OAuth Code Flow Debugger

Trace Authorization Code flow failures across state, PKCE, redirect URI, token exchange, and session boundaries.

Time: 8-11 minutes
Concept: OAuth Authorization Code flow

Play OAuth Code Flow Debugger

Auth Intermediate

Auth Token Inspector

Inspect authentication scenarios and choose safe backend decisions for tokens, scopes, sessions, CSRF, and object-level authorization.

Time: 6-9 minutes
Concept: Authentication, authorization, sessions, and token safety

Play Auth Token Inspector

APIs Intermediate

CORS Preflight Pilot

Guide browser API requests through CORS decisions covering origins, preflight, credentials, exposed headers, and cache safety.

Time: 6-9 minutes
Concept: CORS, browser security boundaries, and preflight response design

Play CORS Preflight Pilot