diff --git a/core/assets/scaffold/files/default.settings.php b/core/assets/scaffold/files/default.settings.php
index 72be7750b93a427526891c4d02068fed3c9a74f6..f3dca008fa380e153e86c2a6bb953b4c030184b5 100644
--- a/core/assets/scaffold/files/default.settings.php
+++ b/core/assets/scaffold/files/default.settings.php
@@ -490,6 +490,29 @@
  */
 # $settings['file_public_path'] = 'sites/default/files';
 
+/**
+ * Additional public file schemes:
+ *
+ * Public schemes are URI schemes that allow download access to all users for
+ * all files within that scheme.
+ *
+ * The "public" scheme is always public, and the "private" scheme is always
+ * private, but other schemes, such as "https", "s3", "example", or others,
+ * can be either public or private depending on the site. By default, they're
+ * private, and access to individual files is controlled via
+ * hook_file_download().
+ *
+ * Typically, if a scheme should be public, a module makes it public by
+ * implementing hook_file_download(), and granting access to all users for all
+ * files. This could be either the same module that provides the stream wrapper
+ * for the scheme, or a different module that decides to make the scheme
+ * public. However, in cases where a site needs to make a scheme public, but
+ * is unable to add code in a module to do so, the scheme may be added to this
+ * variable, the result of which is that system_file_download() grants public
+ * access to all files within that scheme.
+ */
+# $settings['file_additional_public_schemes'] = ['example'];
+
 /**
  * Private file path:
  *
diff --git a/core/lib/Drupal/Core/StreamWrapper/PublicStream.php b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
index e89e43219eab46b3fca9ec4310fe50dfc5d86d57..1747bf37c5f58ecb19582ddbe7d9e5926b0ba330 100644
--- a/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
@@ -115,4 +115,28 @@ public static function basePath($site_path = NULL) {
     return Settings::get('file_public_path', $site_path . '/files');
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected function getLocalPath($uri = NULL) {
+    $path = parent::getLocalPath($uri);
+    if (!$path || (strpos($path, 'vfs://') === 0)) {
+      return $path;
+    }
+
+    if (Settings::get('sa_core_2022_012_override') === TRUE) {
+      return $path;
+    }
+
+    $private_path = Settings::get('file_private_path');
+    if ($private_path) {
+      $private_path = realpath($private_path);
+      if ($private_path && strpos($path, $private_path) === 0) {
+        return FALSE;
+      }
+    }
+
+    return $path;
+  }
+
 }
diff --git a/core/modules/image/src/Controller/ImageStyleDownloadController.php b/core/modules/image/src/Controller/ImageStyleDownloadController.php
index 6ded44fab6b47f63cea902288de181bc6fac99b2..c943452b5b8c2b7ff64d8d3e13097cb61ef51c77 100644
--- a/core/modules/image/src/Controller/ImageStyleDownloadController.php
+++ b/core/modules/image/src/Controller/ImageStyleDownloadController.php
@@ -6,6 +6,7 @@
 use Drupal\Core\File\FileSystemInterface;
 use Drupal\Core\Image\ImageFactory;
 use Drupal\Core\Lock\LockBackendInterface;
+use Drupal\Core\Site\Settings;
 use Drupal\Core\StreamWrapper\StreamWrapperManager;
 use Drupal\Core\StreamWrapper\StreamWrapperManagerInterface;
 use Drupal\image\ImageStyleInterface;
@@ -114,21 +115,25 @@ public function deliver(Request $request, $scheme, ImageStyleInterface $image_st
     $target = $request->query->get('file');
     $image_uri = $scheme . '://' . $target;
 
-    // Check that the style is defined, the scheme is valid, and the image
-    // derivative token is valid. Sites which require image derivatives to be
-    // generated without a token can set the
+    // Check that the style is defined and the scheme is valid.
+    $valid = !empty($image_style) && $this->streamWrapperManager->isValidScheme($scheme);
+
+    // Also validate the derivative token. Sites which require image
+    // derivatives to be generated without a token can set the
     // 'image.settings:allow_insecure_derivatives' configuration to TRUE to
-    // bypass the latter check, but this will increase the site's vulnerability
+    // bypass this check, but this will increase the site's vulnerability
     // to denial-of-service attacks. To prevent this variable from leaving the
     // site vulnerable to the most serious attacks, a token is always required
     // when a derivative of a style is requested.
     // The $target variable for a derivative of a style has
     // styles/<style_name>/... as structure, so we check if the $target variable
     // starts with styles/.
-    $valid = !empty($image_style) && $this->streamWrapperManager->isValidScheme($scheme);
+    $token = $request->query->get(IMAGE_DERIVATIVE_TOKEN, '');
+    $token_is_valid = hash_equals($image_style->getPathToken($image_uri), $token);
     if (!$this->config('image.settings')->get('allow_insecure_derivatives') || strpos(ltrim($target, '\/'), 'styles/') === 0) {
-      $valid &= hash_equals($image_style->getPathToken($image_uri), $request->query->get(IMAGE_DERIVATIVE_TOKEN, ''));
+      $valid = $valid && $token_is_valid;
     }
+
     if (!$valid) {
       // Return a 404 (Page Not Found) rather than a 403 (Access Denied) as the
       // image token is for DDoS protection rather than access checking. 404s
@@ -138,11 +143,23 @@ public function deliver(Request $request, $scheme, ImageStyleInterface $image_st
     }
 
     $derivative_uri = $image_style->buildUri($image_uri);
+    $derivative_scheme = $this->streamWrapperManager->getScheme($derivative_uri);
+
+    if ($token_is_valid) {
+      $is_public = ($scheme !== 'private');
+    }
+    else {
+      $core_schemes = ['public', 'private', 'temporary'];
+      $additional_public_schemes = array_diff(Settings::get('file_additional_public_schemes', []), $core_schemes);
+      $public_schemes = array_merge(['public'], $additional_public_schemes);
+      $is_public = in_array($derivative_scheme, $public_schemes, TRUE);
+    }
+
     $headers = [];
 
-    // If using the private scheme, let other modules provide headers and
+    // If not using a public scheme, let other modules provide headers and
     // control access to the file.
-    if ($scheme == 'private') {
+    if (!$is_public) {
       $headers = $this->moduleHandler()->invokeAll('file_download', [$image_uri]);
       if (in_array(-1, $headers) || empty($headers)) {
         throw new AccessDeniedHttpException();
@@ -150,14 +167,14 @@ public function deliver(Request $request, $scheme, ImageStyleInterface $image_st
     }
 
     // Don't try to generate file if source is missing.
-    if (!file_exists($image_uri)) {
+    if (!$this->sourceImageExists($image_uri, $token_is_valid)) {
       // If the image style converted the extension, it has been added to the
       // original file, resulting in filenames like image.png.jpeg. So to find
       // the actual source image, we remove the extension and check if that
       // image exists.
       $path_info = pathinfo(StreamWrapperManager::getTarget($image_uri));
       $converted_image_uri = sprintf('%s://%s%s%s', $this->streamWrapperManager->getScheme($derivative_uri), $path_info['dirname'], DIRECTORY_SEPARATOR, $path_info['filename']);
-      if (!file_exists($converted_image_uri)) {
+      if (!$this->sourceImageExists($converted_image_uri, $token_is_valid)) {
         $this->logger->notice('Source image at %source_image_path not found while trying to generate derivative image at %derivative_path.', ['%source_image_path' => $image_uri, '%derivative_path' => $derivative_uri]);
         return new Response($this->t('Error generating image, missing source file.'), 404);
       }
@@ -196,9 +213,9 @@ public function deliver(Request $request, $scheme, ImageStyleInterface $image_st
       ];
       // \Drupal\Core\EventSubscriber\FinishResponseSubscriber::onRespond()
       // sets response as not cacheable if the Cache-Control header is not
-      // already modified. We pass in FALSE for non-private schemes for the
-      // $public parameter to make sure we don't change the headers.
-      return new BinaryFileResponse($uri, 200, $headers, $scheme !== 'private');
+      // already modified. When $is_public is TRUE, the following sets the
+      // Cache-Control header to "public".
+      return new BinaryFileResponse($uri, 200, $headers, $is_public);
     }
     else {
       $this->logger->notice('Unable to generate the derived image located at %path.', ['%path' => $derivative_uri]);
@@ -206,4 +223,43 @@ public function deliver(Request $request, $scheme, ImageStyleInterface $image_st
     }
   }
 
+  /**
+   * Checks whether the provided source image exists.
+   *
+   * @param string $image_uri
+   *   The URI for the source image.
+   * @param bool $token_is_valid
+   *   Whether a valid image token was supplied.
+   *
+   * @return bool
+   *   Whether the source image exists.
+   */
+  private function sourceImageExists(string $image_uri, bool $token_is_valid): bool {
+    $exists = file_exists($image_uri);
+
+    // If the file doesn't exist, we can stop here.
+    if (!$exists) {
+      return FALSE;
+    }
+
+    if ($token_is_valid) {
+      return TRUE;
+    }
+
+    if (StreamWrapperManager::getScheme($image_uri) !== 'public') {
+      return TRUE;
+    }
+
+    $image_path = $this->fileSystem->realpath($image_uri);
+    $private_path = Settings::get('file_private_path');
+    if ($private_path) {
+      $private_path = realpath($private_path);
+      if ($private_path && strpos($image_path, $private_path) === 0) {
+        return FALSE;
+      }
+    }
+
+    return TRUE;
+  }
+
 }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index a1b51cc7c0dfb06963a7dd68e8b4a88ac762b58c..deba8f16a016a6ab77d3f8d18261d932119827ed 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -27,6 +27,8 @@
 use Drupal\Core\Queue\QueueGarbageCollectionInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Routing\StackedRouteMatchInterface;
+use Drupal\Core\Site\Settings;
+use Drupal\Core\StreamWrapper\StreamWrapperManager;
 use Drupal\Core\Url;
 use GuzzleHttp\Exception\TransferException;
 use Symfony\Component\HttpFoundation\RedirectResponse;
@@ -1385,3 +1387,21 @@ function system_page_top() {
     }
   }
 }
+
+/**
+ * Implements hook_file_download().
+ */
+function system_file_download($uri) {
+  $core_schemes = ['public', 'private', 'temporary'];
+  $additional_public_schemes = array_diff(Settings::get('file_additional_public_schemes', []), $core_schemes);
+  if ($additional_public_schemes) {
+    $scheme = StreamWrapperManager::getScheme($uri);
+    if (in_array($scheme, $additional_public_schemes, TRUE)) {
+      return [
+        // Returning any header grants access, and setting the 'Cache-Control'
+        // header is appropriate for public files.
+        'Cache-Control' => 'public',
+      ];
+    }
+  }
+}
diff --git a/sites/default/default.settings.php b/sites/default/default.settings.php
index 72be7750b93a427526891c4d02068fed3c9a74f6..f3dca008fa380e153e86c2a6bb953b4c030184b5 100644
--- a/sites/default/default.settings.php
+++ b/sites/default/default.settings.php
@@ -490,6 +490,29 @@
  */
 # $settings['file_public_path'] = 'sites/default/files';
 
+/**
+ * Additional public file schemes:
+ *
+ * Public schemes are URI schemes that allow download access to all users for
+ * all files within that scheme.
+ *
+ * The "public" scheme is always public, and the "private" scheme is always
+ * private, but other schemes, such as "https", "s3", "example", or others,
+ * can be either public or private depending on the site. By default, they're
+ * private, and access to individual files is controlled via
+ * hook_file_download().
+ *
+ * Typically, if a scheme should be public, a module makes it public by
+ * implementing hook_file_download(), and granting access to all users for all
+ * files. This could be either the same module that provides the stream wrapper
+ * for the scheme, or a different module that decides to make the scheme
+ * public. However, in cases where a site needs to make a scheme public, but
+ * is unable to add code in a module to do so, the scheme may be added to this
+ * variable, the result of which is that system_file_download() grants public
+ * access to all files within that scheme.
+ */
+# $settings['file_additional_public_schemes'] = ['example'];
+
 /**
  * Private file path:
  *