Add a `matrix_synapse_url_preview_ip_range_whitelist` variable

roles/custom/matrix-synapse/defaults/main.yml

@@ -778,6 +778,9 @@ matrix_synapse_url_preview_ip_range_blacklist:
   - 'ff00::/8'
   - 'fec0::/10'
 
+# List of IP address CIDR ranges that the URL preview spider is allowed to access even if they are specified in `matrix_synapse_url_preview_ip_range_blacklist`.
+matrix_synapse_url_preview_ip_range_whitelist: []
+
 # A list of values for the Accept-Language HTTP header used when downloading webpages during URL preview generation
 matrix_url_preview_accept_language: ['en-US', 'en']
 

roles/custom/matrix-synapse/templates/synapse/homeserver.yaml.j2

@@ -1141,8 +1141,9 @@ url_preview_ip_range_blacklist: {{ matrix_synapse_url_preview_ip_range_blacklist
 # target IP ranges - e.g. for enabling URL previews for a specific private
 # website only visible in your network.
 #
-#url_preview_ip_range_whitelist:
-#   - '192.168.1.1'
+{% if matrix_synapse_url_preview_enabled %}
+url_preview_ip_range_whitelist: {{ matrix_synapse_url_preview_ip_range_whitelist | to_json }}
+{% endif %}
 
 # Optional list of URL matches that the URL preview spider is
 # denied from accessing.  You should use url_preview_ip_range_blacklist