Add constant for fast requests

INSTALLATION.md

@@ -1490,4 +1490,5 @@ define( 'CONSTANT_NAME', value );
 | FICTIONEER_ENABLE_BROWSER_NOTES | boolean | Whether to inform visitors of missing browser features. Default `false`.
 | FICTIONEER_DEFER_SCRIPTS | boolean | Whether to defer scripts or load them in the footer. Default `true`.
 | FICTIONEER_ENABLE_ASYNC_ONLOAD_PATTERN | boolean | Whether the [onload pattern](https://www.filamentgroup.com/lab/load-css-simpler/) for asynchronous CSS loading is used. Default `true`.
+| FICTIONEER_FAST_REQUESTS | boolean | Whether to enable exiting early for fast AJAX request. Default `true`.
 | FICTIONEER_EXAMPLE_CHAPTER_ICONS | array | Collection of example Font Awesome icon class strings.

functions.php

@@ -396,6 +396,11 @@ if ( ! defined( 'FICTIONEER_ENABLE_ASYNC_ONLOAD_PATTERN' ) ) {
   define( 'FICTIONEER_ENABLE_ASYNC_ONLOAD_PATTERN', true );
 }
 
+// Boolean: Asynchronous loading via onload pattern
+if ( ! defined( 'FICTIONEER_FAST_REQUESTS' ) ) {
+  define( 'FICTIONEER_FAST_REQUESTS', true );
+}
+
 /*
  * Arrays
  */

includes/functions/_setup-wordpress.php

@@ -1380,6 +1380,10 @@ add_filter( 'block_editor_settings_all', 'fictioneer_disable_font_library' );
 /**
  * Accelerate AJAX requests by exiting early
  *
+ * Note: Requests are validated with fictioneer_get_validated_ajax_user(),
+ * making sure that AJAX functions without "_nopriv" are not executed for
+ * unauthenticated users.
+ *
  * @since 5.15.3
  */
 
@@ -1437,6 +1441,12 @@ function fictioneer_fast_ajax() {
   }
 }
 
-if ( isset( $_REQUEST['fcn_fast_ajax'] ) || isset( $_REQUEST['fcn_fast_comment_ajax'] ) ) {
+if (
+  FICTIONEER_FAST_REQUESTS &&
+  (
+    isset( $_REQUEST['fcn_fast_ajax'] ) ||
+    isset( $_REQUEST['fcn_fast_comment_ajax'] )
+  )
+) {
   add_action( 'init', 'fictioneer_fast_ajax', 99999 );
 }