Move the "email unsubscribe" resource, refactor the macaroon generator & simplify the access token verification logic. (#12986)

This simplifies the access token verification logic by removing the `rights`
parameter which was only ever used for the unsubscribe link in email
notifications. The latter has been moved under the `/_synapse` namespace,
since it is not a standard API.

This also makes the email verification link more secure, by embedding the
app_id and pushkey in the macaroon and verifying it. This prevents the user
from tampering the query parameters of that unsubscribe link.

Macaroon generation is refactored:

- Centralised all macaroon generation and verification logic to the
  `MacaroonGenerator`
- Moved to `synapse.utils`
- Changed the constructor to require only a `Clock`, hostname, and a secret key
  (instead of a full `Homeserver`).
- Added tests for all methods.

tests/util/test_macaroons.py

@@ -0,0 +1,146 @@
+# Copyright 2022 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.
+
+from pymacaroons.exceptions import MacaroonVerificationFailedException
+
+from synapse.util.macaroons import MacaroonGenerator, OidcSessionData
+
+from tests.server import get_clock
+from tests.unittest import TestCase
+
+
+class MacaroonGeneratorTestCase(TestCase):
+    def setUp(self):
+        self.reactor, hs_clock = get_clock()
+        self.macaroon_generator = MacaroonGenerator(hs_clock, "tesths", b"verysecret")
+        self.other_macaroon_generator = MacaroonGenerator(
+            hs_clock, "tesths", b"anothersecretkey"
+        )
+
+    def test_guest_access_token(self):
+        """Test the generation and verification of guest access tokens"""
+        token = self.macaroon_generator.generate_guest_access_token("@user:tesths")
+        user_id = self.macaroon_generator.verify_guest_token(token)
+        self.assertEqual(user_id, "@user:tesths")
+
+        # Raises with another secret key
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.other_macaroon_generator.verify_guest_token(token)
+
+        # Check that an old access token without the guest caveat does not work
+        macaroon = self.macaroon_generator._generate_base_macaroon("access")
+        macaroon.add_first_party_caveat(f"user_id = {user_id}")
+        macaroon.add_first_party_caveat("nonce = 0123456789abcdef")
+        token = macaroon.serialize()
+
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.macaroon_generator.verify_guest_token(token)
+
+    def test_delete_pusher_token(self):
+        """Test the generation and verification of delete_pusher tokens"""
+        token = self.macaroon_generator.generate_delete_pusher_token(
+            "@user:tesths", "m.mail", "john@example.com"
+        )
+        user_id = self.macaroon_generator.verify_delete_pusher_token(
+            token, "m.mail", "john@example.com"
+        )
+        self.assertEqual(user_id, "@user:tesths")
+
+        # Raises with another secret key
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.other_macaroon_generator.verify_delete_pusher_token(
+                token, "m.mail", "john@example.com"
+            )
+
+        # Raises when verifying for another pushkey
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.macaroon_generator.verify_delete_pusher_token(
+                token, "m.mail", "other@example.com"
+            )
+
+        # Raises when verifying for another app_id
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.macaroon_generator.verify_delete_pusher_token(
+                token, "somethingelse", "john@example.com"
+            )
+
+        # Check that an old token without the app_id and pushkey still works
+        macaroon = self.macaroon_generator._generate_base_macaroon("delete_pusher")
+        macaroon.add_first_party_caveat("user_id = @user:tesths")
+        token = macaroon.serialize()
+        user_id = self.macaroon_generator.verify_delete_pusher_token(
+            token, "m.mail", "john@example.com"
+        )
+        self.assertEqual(user_id, "@user:tesths")
+
+    def test_short_term_login_token(self):
+        """Test the generation and verification of short-term login tokens"""
+        token = self.macaroon_generator.generate_short_term_login_token(
+            user_id="@user:tesths",
+            auth_provider_id="oidc",
+            auth_provider_session_id="sid",
+            duration_in_ms=2 * 60 * 1000,
+        )
+
+        info = self.macaroon_generator.verify_short_term_login_token(token)
+        self.assertEqual(info.user_id, "@user:tesths")
+        self.assertEqual(info.auth_provider_id, "oidc")
+        self.assertEqual(info.auth_provider_session_id, "sid")
+
+        # Raises with another secret key
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.other_macaroon_generator.verify_short_term_login_token(token)
+
+        # Wait a minute
+        self.reactor.pump([60])
+        # Shouldn't raise
+        self.macaroon_generator.verify_short_term_login_token(token)
+        # Wait another minute
+        self.reactor.pump([60])
+        # Should raise since it expired
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.macaroon_generator.verify_short_term_login_token(token)
+
+    def test_oidc_session_token(self):
+        """Test the generation and verification of OIDC session cookies"""
+        state = "arandomstate"
+        session_data = OidcSessionData(
+            idp_id="oidc",
+            nonce="nonce",
+            client_redirect_url="https://example.com/",
+            ui_auth_session_id="",
+        )
+        token = self.macaroon_generator.generate_oidc_session_token(
+            state, session_data, duration_in_ms=2 * 60 * 1000
+        ).encode("utf-8")
+        info = self.macaroon_generator.verify_oidc_session_token(token, state)
+        self.assertEqual(session_data, info)
+
+        # Raises with another secret key
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.other_macaroon_generator.verify_oidc_session_token(token, state)
+
+        # Should raise with another state
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.macaroon_generator.verify_oidc_session_token(token, "anotherstate")
+
+        # Wait a minute
+        self.reactor.pump([60])
+        # Shouldn't raise
+        self.macaroon_generator.verify_oidc_session_token(token, state)
+        # Wait another minute
+        self.reactor.pump([60])
+        # Should raise since it expired
+        with self.assertRaises(MacaroonVerificationFailedException):
+            self.macaroon_generator.verify_oidc_session_token(token, state)