Validate federation server TLS certificates by default.

changelog.d/5359.feature

+Validate federation server TLS certificates by default (implements [MSC1711](https://github.com/matrix-org/matrix-doc/blob/master/proposals/1711-x509-for-federation.md)).

synapse/config/tls.py

@@ -74,7 +74,7 @@ class TlsConfig(Config):
 
         # Whether to verify certificates on outbound federation traffic
         self.federation_verify_certificates = config.get(
-            "federation_verify_certificates", False,
+            "federation_verify_certificates", True,
         )
 
         # Whitelist of domains to not verify certificates for
@@ -241,12 +241,12 @@ class TlsConfig(Config):
         #
         #tls_private_key_path: "%(tls_private_key_path)s"
 
-        # Whether to verify TLS certificates when sending federation traffic.
+        # Whether to verify TLS server certificates for outbound federation requests.
         #
-        # This currently defaults to `false`, however this will change in
-        # Synapse 1.0 when valid federation certificates will be required.
+        # Defaults to `true`. To disable certificate verification, uncomment the
+        # following line.
         #
-        #federation_verify_certificates: true
+        #federation_verify_certificates: false
 
         # Skip federation certificate verification on the following whitelist
         # of domains.

tests/http/federation/test_matrix_federation_agent.py

@@ -27,6 +27,7 @@ from twisted.web.http import HTTPChannel
 from twisted.web.http_headers import Headers
 from twisted.web.iweb import IPolicyForHTTPS
 
+from synapse.config.homeserver import HomeServerConfig
 from synapse.crypto.context_factory import ClientTLSOptionsFactory
 from synapse.http.federation.matrix_federation_agent import (
     MatrixFederationAgent,
@@ -52,11 +53,16 @@ class MatrixFederationAgentTests(TestCase):
 
         self.well_known_cache = TTLCache("test_cache", timer=self.reactor.seconds)
 
+        # for now, we disable cert verification for the test, since the cert we
+        # present will not be trusted. We should do better here, though.
+        config_dict = default_config("test", parse=False)
+        config_dict["federation_verify_certificates"] = False
+        config = HomeServerConfig()
+        config.parse_config_dict(config_dict)
+
         self.agent = MatrixFederationAgent(
             reactor=self.reactor,
-            tls_client_options_factory=ClientTLSOptionsFactory(
-                default_config("test", parse=True)
-            ),
+            tls_client_options_factory=ClientTLSOptionsFactory(config),
             _well_known_tls_policy=TrustingTLSPolicyForHTTPS(),
             _srv_resolver=self.mock_resolver,
             _well_known_cache=self.well_known_cache,