Minor dendrite tweaks.
--- a/dendrite/server/tasks/main.yaml	Mon Jul 19 21:15:42 2021 -0500
+++ b/dendrite/server/tasks/main.yaml	Sat Jul 24 08:50:40 2021 -0500
@@ -87,7 +87,7 @@
   template:
     src: "dendrite.yaml.j2"
     dest: "{{dendrite_dir}}/{{dendrite_instance}}/dendrite.yaml"
-    mode: "0644"
+    mode: "0600"
     owner: "{{dendrite_user}}"
     group: "{{dendrite_user}}"
   notify: reload service
--- a/dendrite/server/templates/dendrite.yaml.j2	Mon Jul 19 21:15:42 2021 -0500
+++ b/dendrite/server/templates/dendrite.yaml.j2	Sat Jul 24 08:50:40 2021 -0500
@@ -147,7 +147,7 @@
 
   # If set, allows registration by anyone who knows the shared secret, regardless of
   # whether registration is otherwise disabled.
-  registration_shared_secret: ""
+  registration_shared_secret: "{{dendrite_registration_secret}}"
 
   # Whether to require reCAPTCHA for registration.
   enable_registration_captcha: false