fix(auth): tighten userinfo-token cache TTL and metric labelling

Address claude-review round 1 on #919:

- Security: userinfo responses carry no `exp`, so userinfo-validated opaque
  tokens were cached for the 1h default TTL — a revoked/expired token could be
  honored for up to an hour. Cache them for `userinfo_cache_ttl` (5 min)
  instead, and document the bounded-staleness window in the docstring.
- Metrics: when introspection AND userinfo both fail, record
  ("introspect","invalid") + ("userinfo","invalid") separately and set
  validation_method="userinfo" before the userinfo call so a userinfo
  exception caught by the outer handler is attributed correctly.
- Style: use the hasattr(...) + truthy pattern for userinfo_uri, matching the
  introspection block above it.
- Tests: cache-hit allowlist bypass for via-userinfo tokens; short-TTL
  assertion; userinfo timeout / connect-error / malformed-JSON fail-closed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/auth/unified_verifier.py

@@ -79,8 +79,9 @@ class UnifiedTokenVerifier(TokenVerifier):
         # client, e.g. Astrolabe, which the Nextcloud oidc app's introspection
         # endpoint reports inactive cross-client). A 200 from userinfo proves
         # the bearer is a live token for its user regardless of issuing client.
-        self.userinfo_uri: str | None = getattr(settings, "userinfo_uri", None)
-        if self.userinfo_uri:
+        self.userinfo_uri: str | None = None
+        if hasattr(settings, "userinfo_uri") and settings.userinfo_uri:
+            self.userinfo_uri = settings.userinfo_uri
             logger.info(
                 "Userinfo token validation fallback enabled: %s", self.userinfo_uri
             )
@@ -99,6 +100,10 @@ class UnifiedTokenVerifier(TokenVerifier):
         # Token cache: token_hash -> (userinfo, expiry_timestamp)
         self._token_cache: dict[str, tuple[dict[str, Any], float]] = {}
         self.cache_ttl = 3600  # 1 hour default
+        # Userinfo responses carry no token `exp`, so userinfo-validated opaque
+        # tokens fall back to a TTL here. Keep it short: a revoked/expired token
+        # is still honored from cache until this window elapses (no exp to gate).
+        self.userinfo_cache_ttl = 300  # 5 minutes
 
         # NOTE: ALLOWED_MCP_CLIENTS and ALLOWED_MGMT_CLIENT are currently separate
         # env vars to keep the MCP-route and management-API auth surfaces
@@ -370,16 +375,19 @@ class UnifiedTokenVerifier(TokenVerifier):
                 if payload:
                     record_oauth_token_validation("introspect", "valid")
                 else:
+                    record_oauth_token_validation("introspect", "invalid")
                     # Introspection can report opaque tokens minted for a
                     # *different* OIDC client (e.g. Astrolabe) as inactive even
                     # when they are live. Fall back to the userinfo endpoint,
                     # which validates any live bearer regardless of client.
+                    # Update validation_method first so a userinfo exception
+                    # caught by the outer handler is attributed correctly.
+                    validation_method = "userinfo"
                     payload = await self._validate_via_userinfo(token)
                     if payload:
-                        validation_method = "userinfo"
                         record_oauth_token_validation("userinfo", "valid")
                     else:
-                        record_oauth_token_validation("introspect", "invalid")
+                        record_oauth_token_validation("userinfo", "invalid")
                         return None
 
             # Check payload is valid
@@ -593,6 +601,11 @@ class UnifiedTokenVerifier(TokenVerifier):
         and the management-API allowlist is relaxed for this path (authorization
         is still enforced per-user by every management endpoint).
 
+        Security note — bounded staleness: userinfo carries no token ``exp``, so
+        a validated token is cached for ``userinfo_cache_ttl`` (5 min) rather
+        than the 1-hour default. A revoked/expired opaque token may therefore be
+        honored from cache for up to that window before re-validation.
+
         Args:
             token: Bearer token to validate.
 
@@ -688,8 +701,19 @@ class UnifiedTokenVerifier(TokenVerifier):
         # Extract expiration
         exp = payload.get("exp")
         if not exp:
-            logger.warning("No 'exp' claim in token, using default TTL")
-            exp = int(time.time() + self.cache_ttl)
+            # userinfo-validated tokens never carry exp (userinfo describes the
+            # user, not the token). Cache them only briefly so a revoked/expired
+            # opaque token can't be honored for the full hour-long default TTL.
+            if payload.get("_auth_via_userinfo"):
+                ttl = self.userinfo_cache_ttl
+                logger.warning(
+                    "Token validated via userinfo has no 'exp'; caching for %ss only",
+                    ttl,
+                )
+            else:
+                ttl = self.cache_ttl
+                logger.warning("No 'exp' claim in token, using default TTL")
+            exp = int(time.time() + ttl)
 
         # Cache the result with the provided key
         userinfo = {

tests/unit/test_unified_verifier.py

@@ -8,6 +8,7 @@ IdP connections.
 import time
 from unittest.mock import AsyncMock, MagicMock, patch
 
+import httpx
 import jwt
 import pytest
 
@@ -719,3 +720,69 @@ class TestUserinfoFallback:
         assert result is not None
         assert result.client_id == "astrolabe"
         userinfo_mock.assert_not_called()
+
+    async def test_mgmt_cache_hit_also_bypasses_allowlist_for_userinfo_tokens(
+        self, monkeypatch, userinfo_settings
+    ):
+        """A second call (cache hit) with a via-userinfo token still bypasses
+        the allowlist — the stamp is preserved in the cached entry."""
+        import hashlib
+
+        monkeypatch.setenv("ALLOWED_MGMT_CLIENT", "astrolabe")
+        verifier = UnifiedTokenVerifier(userinfo_settings)
+
+        token = "opaque-token-cached"
+        cache_key = f"mgmt:{hashlib.sha256(token.encode()).hexdigest()}"
+        verifier._token_cache[cache_key] = (
+            {"sub": "testuser", "scope": "", "_auth_via_userinfo": True},
+            time.time() + 3600,
+        )
+
+        result = await verifier.verify_token_for_management_api(token)
+        assert result is not None
+        assert result.resource == "testuser"
+
+    async def test_userinfo_token_cached_with_short_ttl(self, userinfo_settings):
+        """userinfo tokens (no exp) get the short userinfo TTL, not the 1h default."""
+        verifier = UnifiedTokenVerifier(userinfo_settings)
+        verifier.userinfo_cache_ttl = 300
+
+        before = time.time()
+        access_token = verifier._create_access_token(
+            "opaque-token", {"sub": "testuser", "_auth_via_userinfo": True}
+        )
+        assert access_token is not None
+        # Expiry should sit within the short userinfo window, well under 1h.
+        assert access_token.expires_at <= int(before + 300) + 2
+        assert access_token.expires_at < int(before + verifier.cache_ttl)
+
+    async def test_validate_via_userinfo_timeout(self, userinfo_settings):
+        verifier = UnifiedTokenVerifier(userinfo_settings)
+        with patch.object(
+            verifier.http_client,
+            "get",
+            AsyncMock(side_effect=httpx.TimeoutException("timeout")),
+        ):
+            result = await verifier._validate_via_userinfo("opaque-token")
+        assert result is None
+
+    async def test_validate_via_userinfo_request_error(self, userinfo_settings):
+        verifier = UnifiedTokenVerifier(userinfo_settings)
+        with patch.object(
+            verifier.http_client,
+            "get",
+            AsyncMock(side_effect=httpx.ConnectError("boom")),
+        ):
+            result = await verifier._validate_via_userinfo("opaque-token")
+        assert result is None
+
+    async def test_validate_via_userinfo_malformed_json(self, userinfo_settings):
+        verifier = UnifiedTokenVerifier(userinfo_settings)
+        mock_resp = MagicMock()
+        mock_resp.status_code = 200
+        mock_resp.json.side_effect = ValueError("not json")
+        with patch.object(
+            verifier.http_client, "get", AsyncMock(return_value=mock_resp)
+        ):
+            result = await verifier._validate_via_userinfo("opaque-token")
+        assert result is None