Add ability to configure ALLOWED_HOSTS for horizon.

This patch add the ability to configure the ALLOWED_HOSTS in
horizon_local_settings.py.

Depends-On: https://review.opendev.org/c/openstack/openstack-ansible-repo_server/+/766257
Change-Id: I9712dc1e9a41757cf71d3d0704e9885493ce1583

defaults/main.yml

@@ -148,6 +148,10 @@ horizon_session_timeout: 1800
 ## Horizon Help URL Path
 horizon_help_url: https://docs.openstack.org/horizon/latest/user/
 
+## Horizon ALLOWED_HOSTS
+horizon_allowed_hosts:
+  - '*'
+
 ## Installation directories
 horizon_lib_dir: "{{ _horizon_lib_dir }}"
 horizon_lib_wsgi_file: "{{ horizon_lib_dir }}/openstack_dashboard/wsgi.py"

releasenotes/notes/add_allowed_hosts-38036c7457afc255.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - Add ``horizon_allowed_hosts`` to be able to configure django ALLOWED_HOSTS.
+    The default is still the same as it was but you can create a list of allowed
+    hosts in ``/etc/openstack_deploy/user_variables.yml``. to set the correct
+    value, see https://docs.djangoproject.com/en/dev/ref/settings/#allowed-hosts
+    for more details.

templates/horizon_local_settings.py.j2

@@ -41,7 +41,7 @@ LOGOUT_URL = '{{ horizon_logout_url }}'
 # with the list of host/domain names that the application can serve.
 # For more information see:
 # https://docs.djangoproject.com/en/dev/ref/settings/#allowed-hosts
-ALLOWED_HOSTS = ['*']
+ALLOWED_HOSTS = [ "{{ horizon_allowed_hosts | join(',') }}" ]
 
 {% if (horizon_enable_ssl | bool) and (horizon_external_ssl | bool) %}
 # Set SSL proxy settings: