Checkpoint: the request firewall

Inside Solution, implement public static class Firewall: 1. Constructor Firewall(Path root, Set<String> allowedHosts); expose public final Path root and public final Set<String> allowedHosts. 2. boolean canRead(String userPath) — canonical containment against root. 3. boolean canCall(String url) — host extraction + allowlist. 4. boolean authenticate(byte[] salt, String password, byte[] stored) — salted recompute + constant-time verify. 5. static String review(java.util.Map<String, String> findings) — given findings like {"sql":"parameterized", "secret":"env", "depends":"audited"}, return "pass" iff every value is one of the accepted controls: sql∈{parameterized}, secret∈{env}, depends∈{audited}; otherwise return the FIRST key whose control is unacceptable. Unknown keys count as unacceptable. 6. static String threatOf(String control) — map each control to the STRIDE letter it primarily addresses: "canonicalization"→"T", "allowlist"→"I", "parameterized"→"T", "least-privilege"→"E", "rate-limit"→"D"; unknown → "?".