fix: options call

src/Controller/DAVController.php

@@ -295,8 +295,26 @@ private function initExceptionListener()
      */
     public function dav(Request $request, string $path)
     {
+        // We need to acknowledge the OPTIONS call before sabre/dav for public
+        // calendars since we're circumventing the lib
         if ('OPTIONS' === $request->getMethod()) {
-            return new Response();
+            $response = new Response();
+
+            // Adapted from CorePlugin's httpOptions()
+            // https://github.com/sabre-io/dav/blob/master/lib/DAV/CorePlugin.php#L210
+            $methods = $this->server->getAllowedMethods("");
+
+            $response->headers->set('Allow', strtoupper(implode(', ', $methods)));
+            $features = ['1', '3', 'extended-mkcol'];
+
+            foreach ($this->server->getPlugins() as $plugin) {
+                $features = array_merge($features, $plugin->getFeatures());
+            }
+
+            $response->headers->set('DAV', implode(', ', $features));
+            $response->headers->set('MS-Author-Via', 'DAV');
+
+            return $response;
         }
 
         // \Sabre\DAV\Server does not let us use a custom SAPI, and its behaviour