Add option to domain source to stop redirection from aliases

domain_source/config/install/domain_source.settings.yml

@@ -1 +1,2 @@
 exclude_routes: {}
+dont_redirect_on_aliases: 0

domain_source/config/schema/domain_source.schema.yml

@@ -8,3 +8,6 @@ domain_source.settings:
       sequence:
         type: string
         label: 'Route'
+    dont_redirect_on_aliases:
+      type: boolean
+      label: 'Stop redirecting on aliases'

domain_source/src/Form/DomainSourceSettingsForm.php

@@ -49,6 +49,11 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#options' => $options,
       '#description' => $this->t('Check the routes to disable. Any entity URL with a Domain Source field will be rewritten unless its corresponding route is disabled.'),
     ];
+    $form['dont_redirect_on_aliases'] = [
+      '#type' => 'checkbox',
+      '#title' => t('Don\'t redirect to the primary domain on aliases'),
+      '#default_value' => $config->get('dont_redirect_on_aliases')
+    ];
     return parent::buildForm($form, $form_state);
   }
 
@@ -58,6 +63,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   public function submitForm(array &$form, FormStateInterface $form_state) {
     $this->config('domain_source.settings')
       ->set('exclude_routes', $form_state->getValue('exclude_routes'))
+      ->set('dont_redirect_on_aliases', $form_state->getValue('dont_redirect_on_aliases'))
       ->save();
 
     parent::submitForm($form, $form_state);

domain_source/src/HttpKernel/DomainSourcePathProcessor.php

@@ -106,6 +106,8 @@ public function __construct(DomainNegotiatorInterface $negotiator, ModuleHandler
    * {@inheritdoc}
    */
   public function processOutbound($path, &$options = [], Request $request = NULL, BubbleableMetadata $bubbleable_metadata = NULL) {
+    $config = $this->configFactory->get('domain_source.settings');
+
     // Load the active domain if not set.
     if (empty($options['active_domain'])) {
       $active_domain = $this->getActiveDomain();
@@ -173,7 +175,7 @@ public function processOutbound($path, &$options = [], Request $request = NULL,
       $this->moduleHandler->alter('domain_source_path', $source, $path, $options);
     }
     // If a source domain is specified, rewrite the link.
-    if (!empty($source)) {
+    if (!empty($source) && (!$config->get('dont_redirect_on_aliases') || ($config->get('dont_redirect_on_aliases') && $source->id() != $options['active_domain']->id()))) {
       // Note that url rewrites add a leading /, which getPath() also adds.
       $options['base_url'] = trim($source->getPath(), '/');
       $options['absolute'] = TRUE;