Stop putting a time caveat on access tokens

The 'time' caveat on the access tokens was something of a lie, since we weren't
enforcing it; more pertinently its presence stops us ever adding useful time
caveats.

Let's move in the right direction by not lying in our caveats.

synapse/api/auth.py

@@ -810,6 +810,10 @@ class Auth(object):
         else:
             v.satisfy_general(lambda c: c.startswith("time < "))
 
+        # access_tokens and refresh_tokens include a nonce for uniqueness: any
+        # value is acceptable
+        v.satisfy_general(lambda c: c.startswith("nonce = "))
+
         v.verify(macaroon, self.hs.config.macaroon_secret_key)
 
     def _verify_expiry(self, caveat):

synapse/config/registration.py

@@ -32,7 +32,6 @@ class RegistrationConfig(Config):
             )
 
         self.registration_shared_secret = config.get("registration_shared_secret")
-        self.user_creation_max_duration = int(config["user_creation_max_duration"])
 
         self.bcrypt_rounds = config.get("bcrypt_rounds", 12)
         self.trusted_third_party_id_servers = config["trusted_third_party_id_servers"]
@@ -55,11 +54,6 @@ class RegistrationConfig(Config):
         # secret, even if registration is otherwise disabled.
         registration_shared_secret: "%(registration_shared_secret)s"
 
-        # Sets the expiry for the short term user creation in
-        # milliseconds. For instance the bellow duration is two weeks
-        # in milliseconds.
-        user_creation_max_duration: 1209600000
-
         # Set the number of bcrypt rounds used to generate password hash.
         # Larger numbers increase the work factor needed to generate the hash.
         # The default number of rounds is 12.

synapse/handlers/auth.py

@@ -538,14 +538,15 @@ class AuthHandler(BaseHandler):
                                                    device_id)
         defer.returnValue(refresh_token)
 
-    def generate_access_token(self, user_id, extra_caveats=None,
+    def generate_access_token(self, user_id, extra_caveats=None):
-                              duration_in_ms=(60 * 60 * 1000)):
         extra_caveats = extra_caveats or []
         macaroon = self._generate_base_macaroon(user_id)
         macaroon.add_first_party_caveat("type = access")
-        now = self.hs.get_clock().time_msec()
+        # Include a nonce, to make sure that each login gets a different
-        expiry = now + duration_in_ms
+        # access token.
-        macaroon.add_first_party_caveat("time < %d" % (expiry,))
+        macaroon.add_first_party_caveat("nonce = %s" % (
+            stringutils.random_string_with_symbols(16),
+        ))
         for caveat in extra_caveats:
             macaroon.add_first_party_caveat(caveat)
         return macaroon.serialize()

synapse/handlers/register.py

@@ -369,7 +369,7 @@ class RegistrationHandler(BaseHandler):
         defer.returnValue(data)
 
     @defer.inlineCallbacks
-    def get_or_create_user(self, requester, localpart, displayname, duration_in_ms,
+    def get_or_create_user(self, requester, localpart, displayname,
                            password_hash=None):
         """Creates a new user if the user does not exist,
         else revokes all previous access tokens and generates a new one.
@@ -399,8 +399,7 @@ class RegistrationHandler(BaseHandler):
 
         user = UserID(localpart, self.hs.hostname)
         user_id = user.to_string()
-        token = self.auth_handler().generate_access_token(
+        token = self.auth_handler().generate_access_token(user_id)
-            user_id, None, duration_in_ms)
 
         if need_register:
             yield self.store.register(

synapse/rest/client/v1/register.py

@@ -384,7 +384,6 @@ class CreateUserRestServlet(ClientV1RestServlet):
     def __init__(self, hs):
         super(CreateUserRestServlet, self).__init__(hs)
         self.store = hs.get_datastore()
-        self.direct_user_creation_max_duration = hs.config.user_creation_max_duration
         self.handlers = hs.get_handlers()
 
     @defer.inlineCallbacks
@@ -418,18 +417,8 @@ class CreateUserRestServlet(ClientV1RestServlet):
         if "displayname" not in user_json:
             raise SynapseError(400, "Expected 'displayname' key.")
 
-        if "duration_seconds" not in user_json:
-            raise SynapseError(400, "Expected 'duration_seconds' key.")
-
         localpart = user_json["localpart"].encode("utf-8")
         displayname = user_json["displayname"].encode("utf-8")
-        duration_seconds = 0
-        try:
-            duration_seconds = int(user_json["duration_seconds"])
-        except ValueError:
-            raise SynapseError(400, "Failed to parse 'duration_seconds'")
-        if duration_seconds > self.direct_user_creation_max_duration:
-            duration_seconds = self.direct_user_creation_max_duration
         password_hash = user_json["password_hash"].encode("utf-8") \
             if user_json.get("password_hash") else None
 
@@ -438,7 +427,6 @@ class CreateUserRestServlet(ClientV1RestServlet):
             requester=requester,
             localpart=localpart,
             displayname=displayname,
-            duration_in_ms=(duration_seconds * 1000),
             password_hash=password_hash
         )
 

tests/handlers/test_auth.py

@@ -61,14 +61,14 @@ class AuthTestCase(unittest.TestCase):
         def verify_type(caveat):
             return caveat == "type = access"
 
-        def verify_expiry(caveat):
+        def verify_nonce(caveat):
-            return caveat == "time < 8600000"
+            return caveat.startswith("nonce =")
 
         v = pymacaroons.Verifier()
         v.satisfy_general(verify_gen)
         v.satisfy_general(verify_user)
         v.satisfy_general(verify_type)
-        v.satisfy_general(verify_expiry)
+        v.satisfy_general(verify_nonce)
         v.verify(macaroon, self.hs.config.macaroon_secret_key)
 
     def test_short_term_login_token_gives_user_id(self):

tests/handlers/test_register.py

@@ -53,13 +53,12 @@ class RegistrationTestCase(unittest.TestCase):
 
     @defer.inlineCallbacks
     def test_user_is_created_and_logged_in_if_doesnt_exist(self):
-        duration_ms = 200
         local_part = "someone"
         display_name = "someone"
         user_id = "@someone:test"
         requester = create_requester("@as:test")
         result_user_id, result_token = yield self.handler.get_or_create_user(
-            requester, local_part, display_name, duration_ms)
+            requester, local_part, display_name)
         self.assertEquals(result_user_id, user_id)
         self.assertEquals(result_token, 'secret')
 
@@ -71,12 +70,11 @@ class RegistrationTestCase(unittest.TestCase):
             user_id=frank.to_string(),
             token="jkv;g498752-43gj['eamb!-5",
             password_hash=None)
-        duration_ms = 200
         local_part = "frank"
         display_name = "Frank"
         user_id = "@frank:test"
         requester = create_requester("@as:test")
         result_user_id, result_token = yield self.handler.get_or_create_user(
-            requester, local_part, display_name, duration_ms)
+            requester, local_part, display_name)
         self.assertEquals(result_user_id, user_id)
         self.assertEquals(result_token, 'secret')