An observed fa_token (via Referer leaks, access logs, JS monitors)
could previously be redeemed against a different reverse-proxied app
within the 60s TTL. The token now stores the destination host at
creation and the verifier rejects mismatches without burning the cache
entry, so legitimate destinations can still redeem.
Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>