Support expiry of refresh tokens and expiry of the overall session when refresh tokens are in use. (#11425)

6 files changed, 213 insertions, 53 deletions

diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index 61e569d412..5e21548060 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -113,14 +113,11 @@ class RegistrationConfig(Config):
         self.session_lifetime = session_lifetime
 
         # The `refreshable_access_token_lifetime` applies for tokens that can be renewed
-        # using a refresh token, as per MSC2918. If it is `None`, the refresh
-        # token mechanism is disabled.
-        #
-        # Since it is incompatible with the `session_lifetime` mechanism, it is set to
-        # `None` by default if a `session_lifetime` is set.
+        # using a refresh token, as per MSC2918.
+        # If it is `None`, the refresh token mechanism is disabled.
         refreshable_access_token_lifetime = config.get(
             "refreshable_access_token_lifetime",
-            "5m" if session_lifetime is None else None,
+            "5m",
         )
         if refreshable_access_token_lifetime is not None:
             refreshable_access_token_lifetime = self.parse_duration(
@@ -128,17 +125,10 @@ class RegistrationConfig(Config):
             )
         self.refreshable_access_token_lifetime = refreshable_access_token_lifetime
 
-        if (
-            session_lifetime is not None
-            and refreshable_access_token_lifetime is not None
-        ):
-            raise ConfigError(
-                "The refresh token mechanism is incompatible with the "
-                "`session_lifetime` option. Consider disabling the "
-                "`session_lifetime` option or disabling the refresh token "
-                "mechanism by removing the `refreshable_access_token_lifetime` "
-                "option."
-            )
+        refresh_token_lifetime = config.get("refresh_token_lifetime")
+        if refresh_token_lifetime is not None:
+            refresh_token_lifetime = self.parse_duration(refresh_token_lifetime)
+        self.refresh_token_lifetime = refresh_token_lifetime
 
         # The fallback template used for authenticating using a registration token
         self.registration_token_template = self.read_template("registration_token.html")
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index 4b66a9862f..4d9c4e5834 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -18,6 +18,7 @@ import time
 import unicodedata
 import urllib.parse
 from binascii import crc32
+from http import HTTPStatus
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -756,53 +757,109 @@ class AuthHandler:
     async def refresh_token(
         self,
         refresh_token: str,
-        valid_until_ms: Optional[int],
-    ) -> Tuple[str, str]:
+        access_token_valid_until_ms: Optional[int],
+        refresh_token_valid_until_ms: Optional[int],
+    ) -> Tuple[str, str, Optional[int]]:
         """
         Consumes a refresh token and generate both a new access token and a new refresh token from it.
 
         The consumed refresh token is considered invalid after the first use of the new access token or the new refresh token.
 
+        The lifetime of both the access token and refresh token will be capped so that they
+        do not exceed the session's ultimate expiry time, if applicable.
+
         Args:
             refresh_token: The token to consume.
-            valid_until_ms: The expiration timestamp of the new access token.
-
+            access_token_valid_until_ms: The expiration timestamp of the new access token.
+                None if the access token does not expire.
+            refresh_token_valid_until_ms: The expiration timestamp of the new refresh token.
+                None if the refresh token does not expire.
         Returns:
-            A tuple containing the new access token and refresh token
+            A tuple containing:
+              - the new access token
+              - the new refresh token
+              - the actual expiry time of the access token, which may be earlier than
+                `access_token_valid_until_ms`.
         """
 
         # Verify the token signature first before looking up the token
         if not self._verify_refresh_token(refresh_token):
-            raise SynapseError(401, "invalid refresh token", Codes.UNKNOWN_TOKEN)
+            raise SynapseError(
+                HTTPStatus.UNAUTHORIZED, "invalid refresh token", Codes.UNKNOWN_TOKEN
+            )
 
         existing_token = await self.store.lookup_refresh_token(refresh_token)
         if existing_token is None:
-            raise SynapseError(401, "refresh token does not exist", Codes.UNKNOWN_TOKEN)
+            raise SynapseError(
+                HTTPStatus.UNAUTHORIZED,
+                "refresh token does not exist",
+                Codes.UNKNOWN_TOKEN,
+            )
 
         if (
             existing_token.has_next_access_token_been_used
             or existing_token.has_next_refresh_token_been_refreshed
         ):
             raise SynapseError(
-                403, "refresh token isn't valid anymore", Codes.FORBIDDEN
+                HTTPStatus.FORBIDDEN,
+                "refresh token isn't valid anymore",
+                Codes.FORBIDDEN,
+            )
+
+        now_ms = self._clock.time_msec()
+
+        if existing_token.expiry_ts is not None and existing_token.expiry_ts < now_ms:
+
+            raise SynapseError(
+                HTTPStatus.FORBIDDEN,
+                "The supplied refresh token has expired",
+                Codes.FORBIDDEN,
             )
 
+        if existing_token.ultimate_session_expiry_ts is not None:
+            # This session has a bounded lifetime, even across refreshes.
+
+            if access_token_valid_until_ms is not None:
+                access_token_valid_until_ms = min(
+                    access_token_valid_until_ms,
+                    existing_token.ultimate_session_expiry_ts,
+                )
+            else:
+                access_token_valid_until_ms = existing_token.ultimate_session_expiry_ts
+
+            if refresh_token_valid_until_ms is not None:
+                refresh_token_valid_until_ms = min(
+                    refresh_token_valid_until_ms,
+                    existing_token.ultimate_session_expiry_ts,
+                )
+            else:
+                refresh_token_valid_until_ms = existing_token.ultimate_session_expiry_ts
+            if existing_token.ultimate_session_expiry_ts < now_ms:
+                raise SynapseError(
+                    HTTPStatus.FORBIDDEN,
+                    "The session has expired and can no longer be refreshed",
+                    Codes.FORBIDDEN,
+                )
+
         (
             new_refresh_token,
             new_refresh_token_id,
         ) = await self.create_refresh_token_for_user_id(
-            user_id=existing_token.user_id, device_id=existing_token.device_id
+            user_id=existing_token.user_id,
+            device_id=existing_token.device_id,
+            expiry_ts=refresh_token_valid_until_ms,
+            ultimate_session_expiry_ts=existing_token.ultimate_session_expiry_ts,
         )
         access_token = await self.create_access_token_for_user_id(
             user_id=existing_token.user_id,
             device_id=existing_token.device_id,
-            valid_until_ms=valid_until_ms,
+            valid_until_ms=access_token_valid_until_ms,
             refresh_token_id=new_refresh_token_id,
         )
         await self.store.replace_refresh_token(
             existing_token.token_id, new_refresh_token_id
         )
-        return access_token, new_refresh_token
+        return access_token, new_refresh_token, access_token_valid_until_ms
 
     def _verify_refresh_token(self, token: str) -> bool:
         """
@@ -836,6 +893,8 @@ class AuthHandler:
         self,
         user_id: str,
         device_id: str,
+        expiry_ts: Optional[int],
+        ultimate_session_expiry_ts: Optional[int],
     ) -> Tuple[str, int]:
         """
         Creates a new refresh token for the user with the given user ID.
@@ -843,6 +902,13 @@ class AuthHandler:
         Args:
             user_id: canonical user ID
             device_id: the device ID to associate with the token.
+            expiry_ts (milliseconds since the epoch): Time after which the
+                refresh token cannot be used.
+                If None, the refresh token never expires until it has been used.
+            ultimate_session_expiry_ts (milliseconds since the epoch):
+                Time at which the session will end and can not be extended any
+                further.
+                If None, the session can be refreshed indefinitely.
 
         Returns:
             The newly created refresh token and its ID in the database
@@ -852,6 +918,8 @@ class AuthHandler:
             user_id=user_id,
             token=refresh_token,
             device_id=device_id,
+            expiry_ts=expiry_ts,
+            ultimate_session_expiry_ts=ultimate_session_expiry_ts,
         )
         return refresh_token, refresh_token_id
 
diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index 448a36108e..8136ae264d 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -119,6 +119,7 @@ class RegistrationHandler:
         self.refreshable_access_token_lifetime = (
             hs.config.registration.refreshable_access_token_lifetime
         )
+        self.refresh_token_lifetime = hs.config.registration.refresh_token_lifetime
 
         init_counters_for_auth_provider("")
 
@@ -793,13 +794,13 @@ class RegistrationHandler:
         class and RegisterDeviceReplicationServlet.
         """
         assert not self.hs.config.worker.worker_app
-        valid_until_ms = None
+        access_token_expiry = None
         if self.session_lifetime is not None:
             if is_guest:
                 raise Exception(
                     "session_lifetime is not currently implemented for guest access"
                 )
-            valid_until_ms = self.clock.time_msec() + self.session_lifetime
+            access_token_expiry = self.clock.time_msec() + self.session_lifetime
 
         refresh_token = None
         refresh_token_id = None
@@ -808,25 +809,52 @@ class RegistrationHandler:
             user_id, device_id, initial_display_name
         )
         if is_guest:
-            assert valid_until_ms is None
+            assert access_token_expiry is None
             access_token = self.macaroon_gen.generate_guest_access_token(user_id)
         else:
             if should_issue_refresh_token:
+                now_ms = self.clock.time_msec()
+
+                # Set the expiry time of the refreshable access token
+                access_token_expiry = now_ms + self.refreshable_access_token_lifetime
+
+                # Set the refresh token expiry time (if configured)
+                refresh_token_expiry = None
+                if self.refresh_token_lifetime is not None:
+                    refresh_token_expiry = now_ms + self.refresh_token_lifetime
+
+                # Set an ultimate session expiry time (if configured)
+                ultimate_session_expiry_ts = None
+                if self.session_lifetime is not None:
+                    ultimate_session_expiry_ts = now_ms + self.session_lifetime
+
+                    # Also ensure that the issued tokens don't outlive the
+                    # session.
+                    # (It would be weird to configure a homeserver with a shorter
+                    # session lifetime than token lifetime, but may as well handle
+                    # it.)
+                    access_token_expiry = min(
+                        access_token_expiry, ultimate_session_expiry_ts
+                    )
+                    if refresh_token_expiry is not None:
+                        refresh_token_expiry = min(
+                            refresh_token_expiry, ultimate_session_expiry_ts
+                        )
+
                 (
                     refresh_token,
                     refresh_token_id,
                 ) = await self._auth_handler.create_refresh_token_for_user_id(
                     user_id,
                     device_id=registered_device_id,
-                )
-                valid_until_ms = (
-                    self.clock.time_msec() + self.refreshable_access_token_lifetime
+                    expiry_ts=refresh_token_expiry,
+                    ultimate_session_expiry_ts=ultimate_session_expiry_ts,
                 )
 
             access_token = await self._auth_handler.create_access_token_for_user_id(
                 user_id,
                 device_id=registered_device_id,
-                valid_until_ms=valid_until_ms,
+                valid_until_ms=access_token_expiry,
                 is_appservice_ghost=is_appservice_ghost,
                 refresh_token_id=refresh_token_id,
             )
@@ -834,7 +862,7 @@ class RegistrationHandler:
         return {
             "device_id": registered_device_id,
             "access_token": access_token,
-            "valid_until_ms": valid_until_ms,
+            "valid_until_ms": access_token_expiry,
             "refresh_token": refresh_token,
         }
 
diff --git a/synapse/rest/client/login.py b/synapse/rest/client/login.py
index 67e03dca04..c982e54156 100644
--- a/synapse/rest/client/login.py
+++ b/synapse/rest/client/login.py
@@ -14,7 +14,17 @@
 
 import logging
 import re
-from typing import TYPE_CHECKING, Any, Awaitable, Callable, Dict, List, Optional, Tuple
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Awaitable,
+    Callable,
+    Dict,
+    List,
+    Optional,
+    Tuple,
+    Union,
+)
 
 from typing_extensions import TypedDict
 
@@ -458,6 +468,7 @@ class RefreshTokenServlet(RestServlet):
         self.refreshable_access_token_lifetime = (
             hs.config.registration.refreshable_access_token_lifetime
         )
+        self.refresh_token_lifetime = hs.config.registration.refresh_token_lifetime
 
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         refresh_submission = parse_json_object_from_request(request)
@@ -467,22 +478,33 @@ class RefreshTokenServlet(RestServlet):
         if not isinstance(token, str):
             raise SynapseError(400, "Invalid param: refresh_token", Codes.INVALID_PARAM)
 
-        valid_until_ms = (
-            self._clock.time_msec() + self.refreshable_access_token_lifetime
-        )
-        access_token, refresh_token = await self._auth_handler.refresh_token(
-            token, valid_until_ms
-        )
-        expires_in_ms = valid_until_ms - self._clock.time_msec()
-        return (
-            200,
-            {
-                "access_token": access_token,
-                "refresh_token": refresh_token,
-                "expires_in_ms": expires_in_ms,
-            },
+        now = self._clock.time_msec()
+        access_valid_until_ms = None
+        if self.refreshable_access_token_lifetime is not None:
+            access_valid_until_ms = now + self.refreshable_access_token_lifetime
+        refresh_valid_until_ms = None
+        if self.refresh_token_lifetime is not None:
+            refresh_valid_until_ms = now + self.refresh_token_lifetime
+
+        (
+            access_token,
+            refresh_token,
+            actual_access_token_expiry,
+        ) = await self._auth_handler.refresh_token(
+            token, access_valid_until_ms, refresh_valid_until_ms
         )
 
+        response: Dict[str, Union[str, int]] = {
+            "access_token": access_token,
+            "refresh_token": refresh_token,
+        }
+
+        # expires_in_ms is only present if the token expires
+        if actual_access_token_expiry is not None:
+            response["expires_in_ms"] = actual_access_token_expiry - now
+
+        return 200, response
+
 
 class SsoRedirectServlet(RestServlet):
     PATTERNS = list(client_patterns("/login/(cas|sso)/redirect$", v1=True)) + [
diff --git a/synapse/storage/databases/main/registration.py b/synapse/storage/databases/main/registration.py
index 0e8c168667..e1ddf06916 100644
--- a/synapse/storage/databases/main/registration.py
+++ b/synapse/storage/databases/main/registration.py
@@ -106,6 +106,15 @@ class RefreshTokenLookupResult:
     has_next_access_token_been_used: bool
     """True if the next access token was already used at least once."""
 
+    expiry_ts: Optional[int]
+    """The time at which the refresh token expires and can not be used.
+    If None, the refresh token doesn't expire."""
+
+    ultimate_session_expiry_ts: Optional[int]
+    """The time at which the session comes to an end and can no longer be
+    refreshed.
+    If None, the session can be refreshed indefinitely."""
+
 
 class RegistrationWorkerStore(CacheInvalidationWorkerStore):
     def __init__(
@@ -1626,8 +1635,10 @@ class RegistrationWorkerStore(CacheInvalidationWorkerStore):
                     rt.user_id,
                     rt.device_id,
                     rt.next_token_id,
-                    (nrt.next_token_id IS NOT NULL) has_next_refresh_token_been_refreshed,
-                    at.used has_next_access_token_been_used
+                    (nrt.next_token_id IS NOT NULL) AS has_next_refresh_token_been_refreshed,
+                    at.used AS has_next_access_token_been_used,
+                    rt.expiry_ts,
+                    rt.ultimate_session_expiry_ts
                 FROM refresh_tokens rt
                 LEFT JOIN refresh_tokens nrt ON rt.next_token_id = nrt.id
                 LEFT JOIN access_tokens at ON at.refresh_token_id = nrt.id
@@ -1648,6 +1659,8 @@ class RegistrationWorkerStore(CacheInvalidationWorkerStore):
                 has_next_refresh_token_been_refreshed=row[4],
                 # This column is nullable, ensure it's a boolean
                 has_next_access_token_been_used=(row[5] or False),
+                expiry_ts=row[6],
+                ultimate_session_expiry_ts=row[7],
             )
 
         return await self.db_pool.runInteraction(
@@ -1915,6 +1928,8 @@ class RegistrationStore(StatsStore, RegistrationBackgroundUpdateStore):
         user_id: str,
         token: str,
         device_id: Optional[str],
+        expiry_ts: Optional[int],
+        ultimate_session_expiry_ts: Optional[int],
     ) -> int:
         """Adds a refresh token for the given user.
 
@@ -1922,6 +1937,13 @@ class RegistrationStore(StatsStore, RegistrationBackgroundUpdateStore):
             user_id: The user ID.
             token: The new access token to add.
             device_id: ID of the device to associate with the refresh token.
+            expiry_ts (milliseconds since the epoch): Time after which the
+                refresh token cannot be used.
+                If None, the refresh token never expires until it has been used.
+            ultimate_session_expiry_ts (milliseconds since the epoch):
+                Time at which the session will end and can not be extended any
+                further.
+                If None, the session can be refreshed indefinitely.
         Raises:
             StoreError if there was a problem adding this.
         Returns:
@@ -1937,6 +1959,8 @@ class RegistrationStore(StatsStore, RegistrationBackgroundUpdateStore):
                 "device_id": device_id,
                 "token": token,
                 "next_token_id": None,
+                "expiry_ts": expiry_ts,
+                "ultimate_session_expiry_ts": ultimate_session_expiry_ts,
             },
             desc="add_refresh_token_to_user",
         )
diff --git a/synapse/storage/schema/main/delta/65/10_expirable_refresh_tokens.sql b/synapse/storage/schema/main/delta/65/10_expirable_refresh_tokens.sql
new file mode 100644
index 0000000000..bdc491c817
--- /dev/null
+++ b/synapse/storage/schema/main/delta/65/10_expirable_refresh_tokens.sql
@@ -0,0 +1,28 @@
+/* Copyright 2021 The Matrix.org Foundation C.I.C
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+ALTER TABLE refresh_tokens
+  -- We add an expiry_ts column (in milliseconds since the Epoch) to refresh tokens.
+  -- They may not be used after they have expired.
+  -- If null, then the refresh token's lifetime is unlimited.
+  ADD COLUMN expiry_ts BIGINT DEFAULT NULL;
+
+ALTER TABLE refresh_tokens
+  -- We also add an ultimate session expiry time (in milliseconds since the Epoch).
+  -- No matter how much the access and refresh tokens are refreshed, they cannot
+  -- be extended past this time.
+  -- If null, then the session length is unlimited.
+  ADD COLUMN ultimate_session_expiry_ts BIGINT DEFAULT NULL;