Remove non-functional 'expire_access_token' setting (#5782)

The `expire_access_token` didn't do what it sounded like it should do. What it
actually did was make Synapse enforce the 'time' caveat on macaroons used as
access tokens, but since our access token macaroons never contained such a
caveat, it was always a no-op.

(The code to add 'time' caveats was removed back in v0.18.5, in #1656)

changelog.d/5782.removal

@@ -0,0 +1 @@
+Remove non-functional 'expire_access_token' setting.

docs/sample_config.yaml

@@ -942,10 +942,6 @@ uploads_path: "DATADIR/uploads"
 #
 # macaroon_secret_key: <PRIVATE STRING>
 
-# Used to enable access token expiration.
-#
-#expire_access_token: False
-
 # a secret which is used to calculate HMACs for form values, to stop
 # falsification of values. Must be specified for the User Consent
 # forms to work.

synapse/api/auth.py

@@ -410,21 +410,16 @@ class Auth(object):
         try:
             user_id = self.get_user_id_from_macaroon(macaroon)
 
-            has_expiry = False
             guest = False
             for caveat in macaroon.caveats:
-                if caveat.caveat_id.startswith("time "):
-                    has_expiry = True
-                elif caveat.caveat_id == "guest = true":
+                if caveat.caveat_id == "guest = true":
                     guest = True
 
-            self.validate_macaroon(
-                macaroon, rights, self.hs.config.expire_access_token, user_id=user_id
-            )
+            self.validate_macaroon(macaroon, rights, user_id=user_id)
         except (pymacaroons.exceptions.MacaroonException, TypeError, ValueError):
             raise InvalidClientTokenError("Invalid macaroon passed.")
 
-        if not has_expiry and rights == "access":
+        if rights == "access":
             self.token_cache[token] = (user_id, guest)
 
         return user_id, guest
@@ -450,7 +445,7 @@ class Auth(object):
                 return caveat.caveat_id[len(user_prefix) :]
         raise InvalidClientTokenError("No user caveat in macaroon")
 
-    def validate_macaroon(self, macaroon, type_string, verify_expiry, user_id):
+    def validate_macaroon(self, macaroon, type_string, user_id):
         """
         validate that a Macaroon is understood by and was signed by this server.
 
@@ -458,7 +453,6 @@ class Auth(object):
             macaroon(pymacaroons.Macaroon): The macaroon to validate
             type_string(str): The kind of token required (e.g. "access",
                               "delete_pusher")
-            verify_expiry(bool): Whether to verify whether the macaroon has expired.
             user_id (str): The user_id required
         """
         v = pymacaroons.Verifier()
@@ -471,19 +465,7 @@ class Auth(object):
         v.satisfy_exact("type = " + type_string)
         v.satisfy_exact("user_id = %s" % user_id)
         v.satisfy_exact("guest = true")
-
-        # verify_expiry should really always be True, but there exist access
-        # tokens in the wild which expire when they should not, so we can't
-        # enforce expiry yet (so we have to allow any caveat starting with
-        # 'time < ' in access tokens).
-        #
-        # On the other hand, short-term login tokens (as used by CAS login, for
-        # example) have an expiry time which we do want to enforce.
-
-        if verify_expiry:
-            v.satisfy_general(self._verify_expiry)
-        else:
-            v.satisfy_general(lambda c: c.startswith("time < "))
+        v.satisfy_general(self._verify_expiry)
 
         # access_tokens include a nonce for uniqueness: any value is acceptable
         v.satisfy_general(lambda c: c.startswith("nonce = "))

synapse/config/key.py

@@ -116,8 +116,6 @@ class KeyConfig(Config):
             seed = bytes(self.signing_key[0])
             self.macaroon_secret_key = hashlib.sha256(seed).digest()
 
-        self.expire_access_token = config.get("expire_access_token", False)
-
         # a secret which is used to calculate HMACs for form values, to stop
         # falsification of values
         self.form_secret = config.get("form_secret", None)
@@ -144,10 +142,6 @@ class KeyConfig(Config):
         #
         %(macaroon_secret_key)s
 
-        # Used to enable access token expiration.
-        #
-        #expire_access_token: False
-
         # a secret which is used to calculate HMACs for form values, to stop
         # falsification of values. Must be specified for the User Consent
         # forms to work.

synapse/handlers/auth.py

@@ -860,7 +860,7 @@ class AuthHandler(BaseHandler):
         try:
             macaroon = pymacaroons.Macaroon.deserialize(login_token)
             user_id = auth_api.get_user_id_from_macaroon(macaroon)
-            auth_api.validate_macaroon(macaroon, "login", True, user_id)
+            auth_api.validate_macaroon(macaroon, "login", user_id)
         except Exception:
             raise AuthError(403, "Invalid token", errcode=Codes.FORBIDDEN)
         self.ratelimit_login_per_account(user_id)

tests/handlers/test_register.py

@@ -44,7 +44,7 @@ class RegistrationTestCase(unittest.HomeserverTestCase):
         hs_config["max_mau_value"] = 50
         hs_config["limit_usage_by_mau"] = True
 
-        hs = self.setup_test_homeserver(config=hs_config, expire_access_token=True)
+        hs = self.setup_test_homeserver(config=hs_config)
         return hs
 
     def prepare(self, reactor, clock, hs):

tests/server_notices/test_resource_limits_server_notices.py

@@ -36,7 +36,7 @@ class TestResourceLimitsServerNotices(unittest.HomeserverTestCase):
             "room_name": "Server Notices",
         }
 
-        hs = self.setup_test_homeserver(config=hs_config, expire_access_token=True)
+        hs = self.setup_test_homeserver(config=hs_config)
         return hs
 
     def prepare(self, reactor, clock, hs):

tests/utils.py

@@ -126,7 +126,6 @@ def default_config(name, parse=False):
         "enable_registration": True,
         "enable_registration_captcha": False,
         "macaroon_secret_key": "not even a little secret",
-        "expire_access_token": False,
         "trusted_third_party_id_servers": [],
         "room_invite_state_types": [],
         "password_providers": [],