defiant/matrix-synapse: require matrix-user role in keycloak

hosts/defiant/services/matrix/synapse.nix

@@ -88,6 +88,10 @@
             localpart_template = "{{ user.preferred_username }}";
             display_name_template = "{{ user.name }}";
           };
+          attribute_requirements = [{
+            attribute = "matrix-roles";
+            value = "matrix-user";
+          }];
           backchannel_logout_enabled = true;
           enable_registration = false;
         }