test(webhook): regression cases for empty-secret HMAC bypass

Covers _reload_dynamic_routes() rejecting empty or missing per-route
secrets when no global fallback exists, preserving the INSECURE_NO_AUTH
opt-in, inheriting a global secret when only the per-route value is
missing, and partial-skip when only one of multiple routes is bad.

tests/gateway/test_webhook_dynamic_routes.py

@@ -6,7 +6,11 @@ import pytest
 from pathlib import Path
 
 from gateway.config import PlatformConfig
-from gateway.platforms.webhook import WebhookAdapter, _DYNAMIC_ROUTES_FILENAME
+from gateway.platforms.webhook import (
+    WebhookAdapter,
+    _DYNAMIC_ROUTES_FILENAME,
+    _INSECURE_NO_AUTH,
+)
 
 
 def _make_adapter(routes=None, extra=None):
@@ -85,3 +89,78 @@ class TestDynamicRouteLoading:
         adapter._reload_dynamic_routes()
         assert "static" in adapter._routes
         assert len(adapter._dynamic_routes) == 0
+
+
+class TestDynamicRouteSecretValidation:
+    """Empty/missing secrets must be rejected during hot-reload.
+
+    Regression for HMAC bypass: prior to the fix, an agent-induced
+    dynamic route with `"secret": ""` would be merged into self._routes
+    by _reload_dynamic_routes(), then _handle_webhook's
+    `if secret and secret != _INSECURE_NO_AUTH` would skip signature
+    validation because empty string is falsy. Unauthenticated POSTs
+    would then execute the webhook prompt.
+    """
+
+    def test_empty_secret_rejected(self, tmp_path):
+        # Explicit empty-string secret must NOT fall back to the global
+        # secret, and the route must be skipped entirely.
+        (tmp_path / _DYNAMIC_ROUTES_FILENAME).write_text(
+            json.dumps({"evil": {"secret": "", "prompt": "rm -rf"}})
+        )
+        adapter = _make_adapter()  # has global secret
+        adapter._reload_dynamic_routes()
+        assert "evil" not in adapter._routes
+        assert "evil" not in adapter._dynamic_routes
+
+    def test_missing_secret_no_global_rejected(self, tmp_path):
+        (tmp_path / _DYNAMIC_ROUTES_FILENAME).write_text(
+            json.dumps({"orphan": {"prompt": "test"}})
+        )
+        # No global secret configured
+        adapter = _make_adapter(extra={"secret": ""})
+        adapter._reload_dynamic_routes()
+        assert "orphan" not in adapter._routes
+        assert "orphan" not in adapter._dynamic_routes
+
+    def test_missing_secret_inherits_global(self, tmp_path):
+        # No per-route secret but a global one is set → route is kept,
+        # the global secret protects it. Preserves existing fallback.
+        (tmp_path / _DYNAMIC_ROUTES_FILENAME).write_text(
+            json.dumps({"valid": {"prompt": "ok"}})
+        )
+        adapter = _make_adapter()  # global secret set
+        adapter._reload_dynamic_routes()
+        assert "valid" in adapter._routes
+
+    def test_insecure_no_auth_preserved(self, tmp_path):
+        # Explicit opt-in escape hatch for local testing — must still load.
+        (tmp_path / _DYNAMIC_ROUTES_FILENAME).write_text(
+            json.dumps({"test": {"secret": _INSECURE_NO_AUTH, "prompt": "p"}})
+        )
+        adapter = _make_adapter()
+        adapter._reload_dynamic_routes()
+        assert "test" in adapter._routes
+
+    def test_warning_logged_on_skip(self, tmp_path, caplog):
+        import logging
+        (tmp_path / _DYNAMIC_ROUTES_FILENAME).write_text(
+            json.dumps({"silent": {"secret": "", "prompt": "x"}})
+        )
+        adapter = _make_adapter()
+        with caplog.at_level(logging.WARNING, logger="gateway.platforms.webhook"):
+            adapter._reload_dynamic_routes()
+        assert any("silent" in rec.message for rec in caplog.records)
+
+    def test_partial_skip(self, tmp_path):
+        # One route bad, one route good — only the bad one is dropped.
+        (tmp_path / _DYNAMIC_ROUTES_FILENAME).write_text(
+            json.dumps({
+                "bad":  {"secret": "", "prompt": "x"},
+                "good": {"secret": "valid-secret", "prompt": "y"},
+            })
+        )
+        adapter = _make_adapter()
+        adapter._reload_dynamic_routes()
+        assert "good" in adapter._routes
+        assert "bad" not in adapter._routes