Import AITURK IDE 1.0.0-beta.1 from Hermes 63279301; preserve MIT license

plugins/cron_providers/chronos/verify.py

@@ -0,0 +1,154 @@
+"""Inbound cron-fire token verification for Chronos (Phase 4E.1).
+
+When NAS relays an external scheduler fire to the agent, it POSTs
+``/api/cron/fire`` with a short-lived NAS-minted JWT. This module verifies that
+JWT before any job runs — the security boundary for remotely-triggered job
+execution.
+
+We verify a NAS-minted JWT (the trust path the agent already has) rather than
+let an external scheduler call the agent directly: the scheduler signs with
+NAS's keys, which the agent doesn't (and shouldn't) hold. See the plan's DQ-4.
+
+The verifier is pluggable (``get_fire_verifier``) so the escape-hatch mode
+(direct per-job cron-key) can swap in later with no handler change.
+
+Crypto is delegated to PyJWT (already a declared dependency) — we do NOT
+hand-roll JWT verification.
+"""
+
+from __future__ import annotations
+
+import logging
+import threading
+from typing import Any, Callable, Dict, Optional
+
+logger = logging.getLogger("cron.chronos.verify")
+
+# The purpose claim that scopes a token to the fire endpoint. A general agent
+# JWT (without this claim) must NOT be replayable against /api/cron/fire.
+_FIRE_PURPOSE = "cron_fire"
+
+# Process-wide cache of PyJWKClient instances, keyed by JWKS URL.
+#
+# WHY THIS EXISTS: a PyJWKClient caches the fetched JWKS (signing keys) on the
+# INSTANCE. Constructing a fresh client per fire therefore threw that cache
+# away and forced a synchronous JWKS HTTP GET to the portal on EVERY fire. Under
+# a burst of concurrent fires (an instance with several cron jobs firing in the
+# same window) that fanned out into N simultaneous JWKS fetches, which the
+# portal rate-limited (HTTP 403) — verification then failed and the agent
+# answered 401. When a fetch was merely slow rather than rate-limited, it blocked
+# the event loop long enough that the fire webhook could not return its 202
+# before the relay's 30s timeout (observed in prod as relay 504s concentrated on
+# high-job-count instances). Reusing one client per URL keeps the signing keys
+# cached (NAS keys rotate rarely), so the steady state is zero JWKS fetches per
+# fire. See docs/chronos-managed-cron-contract.md and the betterstack triage.
+_JWK_CLIENTS: Dict[str, Any] = {}
+_JWK_CLIENTS_LOCK = threading.Lock()
+
+
+def _get_jwk_client(jwks_url: str) -> Any:
+    """Return a process-cached PyJWKClient for ``jwks_url`` (one per URL).
+
+    PyJWKClient does its own key caching internally (``cache_keys``/``lifespan``);
+    the whole point here is to reuse the SAME instance across fires so that cache
+    is actually hit instead of discarded. Double-checked-locked so concurrent
+    fires resolve to a single shared client without racing.
+    """
+    client = _JWK_CLIENTS.get(jwks_url)
+    if client is not None:
+        return client
+    with _JWK_CLIENTS_LOCK:
+        client = _JWK_CLIENTS.get(jwks_url)
+        if client is None:
+            from jwt import PyJWKClient
+
+            # Explicit Accept + User-Agent so the JWKS fetch isn't blocked by the
+            # NAS portal's WAF, which 403s the default Python-urllib fingerprint
+            # (same fix as the dashboard-auth nous/self_hosted providers).
+            client = PyJWKClient(
+                jwks_url,
+                headers={
+                    "Accept": "application/json",
+                    "User-Agent": "HermesAgent/1.0",
+                },
+            )
+            _JWK_CLIENTS[jwks_url] = client
+        return client
+
+
+def verify_nas_fire_token(
+    *,
+    token: str,
+    expected_audience: str,
+    jwks_or_key: Optional[str] = None,
+    issuer: Optional[str] = None,
+    leeway_seconds: int = 30,
+) -> Optional[Dict[str, Any]]:
+    """Verify a NAS-minted cron-fire JWT. Return decoded claims, or None.
+
+    Checks (all must pass):
+      - signature against the NAS JWKS (``jwks_or_key`` is a JWKS URL) — RS256
+        family; symmetric secrets are rejected (NAS signs asymmetrically).
+      - ``aud`` == ``expected_audience`` (this agent: ``agent:{instance_id}``).
+      - ``exp`` / ``nbf`` within ``leeway_seconds``.
+      - ``iss`` == ``issuer`` when an issuer is configured.
+      - ``purpose`` == ``"cron_fire"`` — so a general agent JWT can't be
+        replayed against the fire endpoint.
+
+    Returns None (never raises) on any failure, so the handler can answer 401
+    without leaking which check failed.
+    """
+    if not token or not expected_audience:
+        return None
+    if not jwks_or_key:
+        # No verification key configured → cannot verify → refuse. We never
+        # fall back to unsigned decode for a security boundary.
+        logger.warning("cron fire: no JWKS/key configured; refusing token")
+        return None
+
+    try:
+        import jwt
+
+        # Resolve the signing key from the JWKS endpoint by the token's kid.
+        signing_key = None
+        if jwks_or_key.startswith("http://") or jwks_or_key.startswith("https://"):
+            # Reuse a process-cached client so the JWKS fetch is amortised across
+            # fires (a fresh client per fire re-fetched the JWKS every time and,
+            # under concurrent fires, tripped the portal's rate limit → 403 →
+            # 401, or blocked the event loop past the relay's 30s timeout → 504).
+            jwk_client = _get_jwk_client(jwks_or_key)
+            signing_key = jwk_client.get_signing_key_from_jwt(token).key
+        else:
+            # A PEM public key passed inline (test / pinned-key deployments).
+            signing_key = jwks_or_key
+
+        options = {"require": ["exp", "aud"]}
+        decode_kwargs: Dict[str, Any] = dict(
+            algorithms=["RS256", "RS384", "RS512", "ES256", "ES384"],
+            audience=expected_audience,
+            leeway=leeway_seconds,
+            options=options,
+        )
+        if issuer:
+            decode_kwargs["issuer"] = issuer
+
+        claims = jwt.decode(token, signing_key, **decode_kwargs)
+    except Exception as e:
+        logger.warning("cron fire: token verification failed: %s", e)
+        return None
+
+    if claims.get("purpose") != _FIRE_PURPOSE:
+        logger.warning("cron fire: token missing/!=%s purpose claim", _FIRE_PURPOSE)
+        return None
+
+    return claims
+
+
+def get_fire_verifier() -> Callable[..., Optional[Dict[str, Any]]]:
+    """Return the active inbound-fire verifier.
+
+    Default = the NAS-JWT verifier. The DQ-4 escape hatch (direct per-job
+    cron-key) would return a cron-key verifier here instead, selected by config
+    — so the webhook handler never changes when the auth mode is swapped.
+    """
+    return verify_nas_fire_token