Make sample config allowed_local_3pids regex stricter. (#9719)

The regex should be terminated so that subdomain matches of another
domain are not accepted. Just ensuring that someone doesn't shoot
themselves in the foot by copying our example.

Signed-off-by: Denis Kasak <dkasak@termina.org.uk>

changelog.d/9719.doc

@@ -0,0 +1 @@
+Make the allowed_local_3pids regex example in the sample config stricter.

docs/sample_config.yaml

@@ -1246,9 +1246,9 @@ account_validity:
 #
 #allowed_local_3pids:
 #  - medium: email
-#    pattern: '.*@matrix\.org'
+#    pattern: '^[^@]+@matrix\.org$'
 #  - medium: email
-#    pattern: '.*@vector\.im'
+#    pattern: '^[^@]+@vector\.im$'
 #  - medium: msisdn
 #    pattern: '\+44'
 

synapse/config/registration.py

@@ -298,9 +298,9 @@ class RegistrationConfig(Config):
         #
         #allowed_local_3pids:
         #  - medium: email
-        #    pattern: '.*@matrix\\.org'
+        #    pattern: '^[^@]+@matrix\\.org$'
         #  - medium: email
-        #    pattern: '.*@vector\\.im'
+        #    pattern: '^[^@]+@vector\\.im$'
         #  - medium: msisdn
         #    pattern: '\\+44'