Errors reference

goauth returns JSON errors with a kind field (Auth.js-style).

Common kinds

Kind	When
Configuration	Invalid setup, unknown provider
AccessDenied	SignIn callback returned false
Verification	Bad token, passkey verify failed, OTP wrong
CredentialsSignin	Authorize failed
MFARequired	MFA challenge issued (informational)
MFAVerification	MFA step failed
AdapterError	Database adapter failure
UnknownAction	Invalid route

Example response

{
  "message": "verify assertion",
  "kind": "Verification"
}

Handling in clients

const res = await fetch("/auth/callback/passkey", { method: "POST", body });
if (!res.ok) {
  const err = await res.json();
  if (err.kind === "Verification") {
    // show passkey retry UI
  }
}

Use errors.Is with sentinel errors (ErrMissingAdapter, etc.) in Go middleware wrapping the handler.