add CORS

hosts/www/nginx.nix

@@ -83,6 +83,9 @@ in
         "~ ^/calendars/([^/]+\.ics)$" = {
           alias = "/srv/http/calendars/$1";
           extraConfig = ''
+            if ($http_origin ~ '^https://(www\.)?berlin\.ccc\.de$') {
+              add_header Access-Control-Allow-Origin $http_origin always;
+            }
             add_header Cache-Control "no-cache";
             types {
               text/calendar ics;