Practical writing on OAuth2, OpenID Connect, passkeys, and token security — the problems you hit at 2am, not the happy path.
Subscribe via RSS·5 min read
Your token looks fine, decodes cleanly, and still fails verification. Here are the eight things that actually cause it, in the order worth checking them.
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OAuth2 is authorization, OIDC is authentication built on top of it. Here's what that means concretely, and why using an access token to identify a user is a real vulnerability.
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PKCE is not just for mobile apps anymore. Here's the concrete attack it prevents, why the client secret doesn't save you, and why the spec now recommends it for every OAuth2 client.
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TOTP and SMS codes make phishing harder. Passkeys make it structurally impossible. The difference is origin binding, and it's worth understanding before choosing.
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The error says the URI doesn't match a registered value. Matching is exact string comparison, which makes the causes narrow and mostly invisible — trailing slashes, ports, casing, and encoding.
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Rotation plus reuse detection is the right design. It also logs users out at random if your client can fire two refreshes at once — here's why, and the two ways to fix it.
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localStorage, cookies, memory, or a backend-for-frontend. Every option trades XSS exposure against CSRF exposure and complexity — here's the actual tradeoff rather than the usual dogma.
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Key rotation fails when the new key starts signing before consumers have seen it. The fix is an overlap window sized by your cache TTL and token lifetime — here's the sequence.
·4 min read
OAuth2 scopes answer what an application may do. Roles answer what a user may do. Neither answers whether this user may edit that specific document — and cramming it into a token is how you get 8KB headers.
AuthAction handles token issuance, rotation, JWKS, passkeys, and enterprise SSO — so most of what we write about here stops being your problem.
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