ejabberd: Add support for external authentication cache

ejabberd/templates/ejabberd.yml.erb

@@ -82,6 +82,10 @@ auth_method:
 auth_method: <%= @auth %>
 <% end -%>
 <% if @extauth -%>
+<%   unless @extauth_cache == false or (@auth.is_a?(Array) and @auth.include?('internal') or @auth == 'internal') -%>
+auth_password_format: scram
+extauth_cache: <%= @extauth_cache %>
+<%   end -%>
 extauth_program: "<%= @extauth %>"
 <% end -%>
 <% if @ldap_server -%>