Cache token introspection response from OIDC provider

changelog.d/16117.misc

@@ -0,0 +1 @@
+Cache token introspection response from OIDC provider.

synapse/api/auth/msc3861_delegated.py

@@ -39,6 +39,7 @@
 from synapse.types import Requester, UserID, create_requester
 from synapse.util import json_decoder
 from synapse.util.caches.cached_call import RetryOnExceptionCachedCall
+from synapse.util.caches.expiringcache import ExpiringCache
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -106,6 +107,14 @@ def __init__(self, hs: "HomeServer"):
 
         self._issuer_metadata = RetryOnExceptionCachedCall(self._load_metadata)
 
+        self._clock = hs.get_clock()
+        self._token_cache: ExpiringCache[str, IntrospectionToken] = ExpiringCache(
+            cache_name="introspection_token_cache",
+            clock=self._clock,
+            max_len=10000,
+            expiry_ms=5 * 60 * 1000,
+        )
+
         if isinstance(auth_method, PrivateKeyJWTWithKid):
             # Use the JWK as the client secret when using the private_key_jwt method
             assert self._config.jwk, "No JWK provided"
@@ -144,50 +153,75 @@ async def _introspect_token(self, token: str) -> IntrospectionToken:
         Returns:
             The introspection response
         """
-        metadata = await self._issuer_metadata.get()
-        introspection_endpoint = metadata.get("introspection_endpoint")
-        raw_headers: Dict[str, str] = {
-            "Content-Type": "application/x-www-form-urlencoded",
-            "User-Agent": str(self._http_client.user_agent, "utf-8"),
-            "Accept": "application/json",
-        }
-
-        args = {"token": token, "token_type_hint": "access_token"}
-        body = urlencode(args, True)
-
-        # Fill the body/headers with credentials
-        uri, raw_headers, body = self._client_auth.prepare(
-            method="POST", uri=introspection_endpoint, headers=raw_headers, body=body
-        )
-        headers = Headers({k: [v] for (k, v) in raw_headers.items()})
-
-        # Do the actual request
-        # We're not using the SimpleHttpClient util methods as we don't want to
-        # check the HTTP status code, and we do the body encoding ourselves.
-        response = await self._http_client.request(
-            method="POST",
-            uri=uri,
-            data=body.encode("utf-8"),
-            headers=headers,
-        )
+        # check the cache before doing a request
+        introspection_token = self._token_cache.get(token, None)
+
+        expired = False
+        if introspection_token:
+            # check the expiration field of the token (if it exists)
+            exp = introspection_token.get("exp", None)
+            if exp:
+                time_now = self._clock.time_msec()
+                expired = time_now > exp
+
+        if not introspection_token or expired:
+            metadata = await self._issuer_metadata.get()
+            introspection_endpoint = metadata.get("introspection_endpoint")
+            raw_headers: Dict[str, str] = {
+                "Content-Type": "application/x-www-form-urlencoded",
+                "User-Agent": str(self._http_client.user_agent, "utf-8"),
+                "Accept": "application/json",
+            }
+
+            args = {"token": token, "token_type_hint": "access_token"}
+            body = urlencode(args, True)
+
+            # Fill the body/headers with credentials
+            uri, raw_headers, body = self._client_auth.prepare(
+                method="POST",
+                uri=introspection_endpoint,
+                headers=raw_headers,
+                body=body,
+            )
+            headers = Headers({k: [v] for (k, v) in raw_headers.items()})
+
+            # Do the actual request
+            # We're not using the SimpleHttpClient util methods as we don't want to
+            # check the HTTP status code, and we do the body encoding ourselves.
+            response = await self._http_client.request(
+                method="POST",
+                uri=uri,
+                data=body.encode("utf-8"),
+                headers=headers,
+            )
 
-        resp_body = await make_deferred_yieldable(readBody(response))
+            resp_body = await make_deferred_yieldable(readBody(response))
 
-        if response.code < 200 or response.code >= 300:
-            raise HttpResponseException(
-                response.code,
-                response.phrase.decode("ascii", errors="replace"),
-                resp_body,
-            )
+            if response.code < 200 or response.code >= 300:
+                raise HttpResponseException(
+                    response.code,
+                    response.phrase.decode("ascii", errors="replace"),
+                    resp_body,
+                )
 
-        resp = json_decoder.decode(resp_body.decode("utf-8"))
+            resp = json_decoder.decode(resp_body.decode("utf-8"))
 
-        if not isinstance(resp, dict):
-            raise ValueError(
-                "The introspection endpoint returned an invalid JSON response."
-            )
+            if not isinstance(resp, dict):
+                raise ValueError(
+                    "The introspection endpoint returned an invalid JSON response."
+                )
+
+            expiration = resp.get("exp", None)
+            if expiration:
+                if self._clock.time_msec() > expiration:
+                    raise InvalidClientTokenError("Token is expired.")
+
+            introspection_token = IntrospectionToken(**resp)
+
+            # add token to cache
+            self._token_cache[token] = introspection_token
 
-        return IntrospectionToken(**resp)
+        return introspection_token
 
     async def is_server_admin(self, requester: Requester) -> bool:
         return "urn:synapse:admin:*" in requester.scope

tests/handlers/test_oauth_delegation.py

@@ -491,6 +491,68 @@ def test_unavailable_introspection_endpoint(self) -> None:
         error = self.get_failure(self.auth.get_user_by_req(request), SynapseError)
         self.assertEqual(error.value.code, 503)
 
+    def test_introspection_token_cache(self) -> None:
+        access_token = "open_sesame"
+        self.http_client.request = simple_async_mock(
+            return_value=FakeResponse.json(
+                code=200,
+                payload={"active": "true", "scope": "guest", "jti": access_token},
+            )
+        )
+
+        # first call should cache response - check cache
+        # Mpyp ignores below are due to mypy not understanding the dynamic substitution of msc3861 auth code
+        # for regular auth code via the config
+        self.get_success(
+            self.auth._introspect_token(access_token)  # type: ignore[attr-defined]
+        )
+        introspection_token = self.auth._token_cache.get(access_token)  # type: ignore[attr-defined]
+        self.assertEqual(introspection_token["jti"], access_token)
+        # there's been one http request
+        self.http_client.request.assert_called_once()
+
+        # second call should pull from cache, there should still be only one http request
+        token = self.get_success(self.auth._introspect_token(access_token))  # type: ignore[attr-defined]
+        self.http_client.request.assert_called_once()
+        self.assertEqual(token["jti"], access_token)
+
+        # advance past five minutes and check that cache expired - there should be more than one http call now
+        self.reactor.advance(360)
+        token_2 = self.get_success(self.auth._introspect_token(access_token))  # type: ignore[attr-defined]
+        self.assertEqual(self.http_client.request.call_count, 2)
+        self.assertEqual(token_2["jti"], access_token)
+
+        # test that if a cached token is expired, a fresh token will be pulled from authorizing server - first add a
+        # token with a soon-to-expire `exp` field to the cache
+        self.http_client.request = simple_async_mock(
+            return_value=FakeResponse.json(
+                code=200,
+                payload={
+                    "active": "true",
+                    "scope": "guest",
+                    "jti": "stale",
+                    "exp": self.clock.time_msec() + 100,
+                },
+            )
+        )
+        self.get_success(
+            self.auth._introspect_token("stale")  # type: ignore[attr-defined]
+        )
+        introspection_token = self.auth._token_cache.get("stale")  # type: ignore[attr-defined]
+        self.assertEqual(introspection_token["jti"], "stale")
+        self.assertEqual(self.http_client.request.call_count, 1)
+
+        # advance the reactor past the token expiry but less than the cache expiry
+        self.reactor.advance(30)
+        self.assertEqual(self.auth._token_cache.get("stale"), introspection_token)  # type: ignore[attr-defined]
+
+        # check that the next call causes another http request (which will fail because the token is technically expired
+        # but the important thing is we discard the token from the cache and try the network)
+        self.get_failure(
+            self.auth._introspect_token("stale"), InvalidClientTokenError  # type: ignore[attr-defined]
+        )
+        self.assertEqual(self.http_client.request.call_count, 2)
+
     def make_device_keys(self, user_id: str, device_id: str) -> JsonDict:
         # We only generate a master key to simplify the test.
         master_signing_key = generate_signing_key(device_id)