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Auth 20 errors

Authentication & SSO Errors

OIDC, SAML, Auth0, Okta, Keycloak, passkeys and MFA failures.

Understanding Auth errors

Identity errors are almost always configuration mismatches between two systems rather than code bugs: a redirect URI registered with a trailing slash, a client secret that was rotated on one side only, a clock that has drifted past the token skew allowance. Because the identity provider deliberately returns vague errors to avoid leaking information to attackers, the provider's own log is usually far more informative than the message your application receives.

How to debug Auth errors

  1. Open the identity provider's log or event stream first. Auth0, Okta and Keycloak all record a detailed reason that they never send back to the client.
  2. Compare the redirect URI byte for byte, including scheme, port and trailing slash. http://localhost:3000/callback and http://localhost:3000/callback/ are different URIs.
  3. Decode the token rather than guessing. Paste it into a local JWT decoder and check iss, aud, exp and nbf, never a remote paste site, because tokens are credentials.
  4. Check clock skew with timedatectl or ntpq -p. Kerberos, SAML and JWT all reject tokens outside a tight time window, and a drifting VM clock produces intermittent, unreproducible auth failures.
  5. For passkeys and WebAuthn, verify the Relying Party ID matches the origin exactly and that the page is served over HTTPS or on localhost. Nothing else is a secure context.

Tools worth reaching for

  • Provider audit logs
  • jwt decoding (locally)
  • openssl x509 -noout -text
  • browser devtools network tab

All 20 Auth errors

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