Index: config/schema/url_embed.schema.yml
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/config/schema/url_embed.schema.yml b/config/schema/url_embed.schema.yml
new file mode 100644
--- /dev/null	(revision 515020552861edaf2f104b03eb7db26f9276ef21)
+++ b/config/schema/url_embed.schema.yml	(revision 515020552861edaf2f104b03eb7db26f9276ef21)
@@ -0,0 +1,10 @@
+url_embed.settings:
+  type: config_object
+  label: 'Url Embed config.'
+  mapping:
+    facebook_app_id:
+      type: string
+      label: 'Facebook App ID'
+    facebook_app_secret:
+      type: string
+      label: 'Facebook App Secret'
Index: src/Form/UrlEmbedAdminSettingsForm.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/src/Form/UrlEmbedAdminSettingsForm.php b/src/Form/UrlEmbedAdminSettingsForm.php
new file mode 100644
--- /dev/null	(revision 515020552861edaf2f104b03eb7db26f9276ef21)
+++ b/src/Form/UrlEmbedAdminSettingsForm.php	(revision 515020552861edaf2f104b03eb7db26f9276ef21)
@@ -0,0 +1,88 @@
+<?php
+
+namespace Drupal\url_embed\Form;
+
+use Drupal\Core\Form\ConfigFormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Configure Url Embed settings for this site.
+ */
+class UrlEmbedAdminSettingsForm extends ConfigFormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'url_embed_admin_settings';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEditableConfigNames() {
+    return ['url_embed.settings'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $config = $this->config('url_embed.settings');
+
+    $form['facebook_app'] = [
+      '#type' => 'details',
+      '#open' => TRUE,
+      '#title' => $this->t('Facebook / Instagram App'),
+      '#description' => $this->t('As of Oct 24 2020, Facebook and Instagram require you to create a live <a href="@doc_url" target="_blank">facebook app with an oEmbed product enabled</a> to embed posts.', [
+        '@doc_url' => 'https://developers.facebook.com/docs/plugins/oembed',
+      ]),
+    ];
+
+    // If we have Facebook credentials in the config, check that it is a valid app and show a message to the user.
+    if (!empty($config->get('facebook_app_id')) && !empty($config->get('facebook_app_id'))) {
+      $debug = url_embed_debug_facebook_access_token($config->get('facebook_app_id') . '|' . $config->get('facebook_app_secret'));
+      if (!empty($debug['is_valid'])) {
+        $form['facebook_app']['facebook_app_status']['#markup'] = '<div class="messages messages--status">' . $this->t('The Facebook app is active.') . '</div>';
+      }
+      else {
+        $form['facebook_app']['facebook_app_status']['#markup'] = '<div class="messages messages--warning">' . $this->t('The App ID and App Secret combination is invalid. Make sure you entered your app credentials correctly.') . '</div>';
+      }
+    }
+
+    $form['facebook_app']['facebook_app_id'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('App ID'),
+      '#default_value' => $config->get('facebook_app_id'),
+    ];
+
+    $form['facebook_app']['facebook_app_secret'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('App Secret'),
+      '#default_value' => $config->get('facebook_app_secret'),
+    ];
+
+    return parent::buildForm($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $config = $this->config('url_embed.settings');
+    $config
+      ->set('facebook_app_id', $form_state->getValue('facebook_app_id'))
+      ->set('facebook_app_secret', $form_state->getValue('facebook_app_secret'))
+      ->save();
+
+    parent::submitForm($form, $form_state);
+  }
+
+}
Index: src/UrlEmbed.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/src/UrlEmbed.php b/src/UrlEmbed.php
--- a/src/UrlEmbed.php	(revision c3469227d337723507b5d1409e2a483efb7daadf)
+++ b/src/UrlEmbed.php	(revision 515020552861edaf2f104b03eb7db26f9276ef21)
@@ -46,13 +46,24 @@
   public $config;

   /**
-   * @{inheritdoc}
+   * Constructs a UrlEmbed object.
+   *
+   * @param array $config
+   *   (optional) The options passed to the adapter.
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   *   (optional) The config factory.
    */
   public function __construct(CacheBackendInterface $cache_backend, TimeInterface $time, ConfigFactoryInterface $config_factory, array $config = []) {
-    $this->config = $config;
     $this->cacheBackend = $cache_backend;
     $this->time = $time;
     $this->configFactory = $config_factory;
+    $global_config = $config_factory->get('url_embed.settings');
+    $defaults = [];
+
+    if ($global_config->get('facebook_app_id') && $global_config->get('facebook_app_secret')) {
+      $defaults['facebook']['key'] = $global_config->get('facebook_app_id') . '|' . $global_config->get('facebook_app_secret');
+    }
+    $this->config = array_replace_recursive($defaults, $config);
   }

   /**
@@ -73,7 +84,7 @@
    * @{inheritdoc}
    */
   public function getEmbed($request, array $config = []) {
-    return Embed::create($request, $config ?: $this->config);
+    return Embed::create($request, array_replace_recursive($this->config, $config));
   }

   /**
Index: url_embed.install
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/url_embed.install b/url_embed.install
--- a/url_embed.install	(revision c3469227d337723507b5d1409e2a483efb7daadf)
+++ b/url_embed.install	(revision 515020552861edaf2f104b03eb7db26f9276ef21)
@@ -24,6 +24,28 @@
       ];
     }
   }
+  elseif ($phase == 'runtime') {
+    $requirements['url_embed']['title'] = t('Url Embed: Facebook/Instagram App');
+    $config = \Drupal::service('config.factory')->get('url_embed.settings');
+    if (empty($config->get('facebook_app_id')) || empty($config->get('facebook_app_secret'))) {
+      $requirements['url_embed']['value'] = t('Missing Facebook app credentials.');
+      $requirements['url_embed']['description'] = t('In order to embed Facebook and Instagram posts you must create a <a href="@facebook_url">live facebook app with oEmbed enabled</a> and add the app ID and Secret to the <a href="@settings_url">Url Embed settings page</a>.',
+        [
+          '@facebook_url' => 'https://developers.facebook.com/docs/plugins/oembed',
+          '@settings_url' => '/admin/config/media/url_embed',
+        ]);
+      $requirements['url_embed']['severity'] = REQUIREMENT_WARNING;
+    }
+    else {
+      $access_token = url_embed_debug_facebook_access_token($config->get('facebook_app_id') . '|' . $config->get('facebook_app_secret'));
+      $is_valid = !empty($access_token['is_valid']);
+      $requirements['url_embed']['value'] = $is_valid ? t('Active') : t('Invalid Facebook app credentials provided.');
+      $requirements['url_embed']['severity'] = $is_valid ? REQUIREMENT_INFO : REQUIREMENT_ERROR;
+      if (!$is_valid) {
+        $requirements['url_embed']['description'] = t('Check that you have entered your app credentials correctly and that it is live. <a href="@settings_url">Edit settings</a>', ['@settings_url' => '/admin/config/media/url_embed']);
+      }
+    }
+  }

   return $requirements;
 }
Index: url_embed.module
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/url_embed.module b/url_embed.module
--- a/url_embed.module	(revision c3469227d337723507b5d1409e2a483efb7daadf)
+++ b/url_embed.module	(revision 515020552861edaf2f104b03eb7db26f9276ef21)
@@ -1,1 +1,41 @@
 <?php
+
+/**
+ * @file
+ * Allows URLs to be embedded using a text editor.
+ */
+
+use Drupal\Component\Serialization\Json;
+
+/**
+ * Performs a GET request to Facebook's graph API to retrieve token debug info.
+ *
+ * @param string $token
+ *   The Facebook access token in the format of "APP_ID|APP_SECRET".
+ *
+ * @return false|array
+ *   An array containing app details if successful, false otherwise.
+ *
+ * @see https://developers.facebook.com/docs/facebook-login/access-tokens/debugging-and-error-handling/
+ */
+function url_embed_debug_facebook_access_token($token) {
+  $url = 'https://graph.facebook.com/v8.0/debug_token?input_token=' . $token . '&access_token=' . $token;
+
+  try {
+    $response = \Drupal::httpClient()->get($url);
+    $code = $response->getStatusCode();
+
+    if ($code == 200) {
+      $data = $response->getBody()->getContents();
+      $decoded = Json::decode($data);
+      return isset($decoded['data']) ? $decoded['data'] : FALSE;
+    }
+    else {
+      return FALSE;
+    }
+  }
+  catch (Exception $e) {
+  }
+
+  return FALSE;
+}
Index: url_embed.routing.yml
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/url_embed.routing.yml b/url_embed.routing.yml
--- a/url_embed.routing.yml	(revision c3469227d337723507b5d1409e2a483efb7daadf)
+++ b/url_embed.routing.yml	(revision 515020552861edaf2f104b03eb7db26f9276ef21)
@@ -5,3 +5,10 @@
     _title: 'Embed URL'
   requirements:
     _embed_button_editor_access: 'TRUE'
+url_embed.admin:
+  path: '/admin/config/media/url_embed'
+  defaults:
+    _form: '\Drupal\url_embed\Form\UrlEmbedAdminSettingsForm'
+    _title: 'Url Embed'
+  requirements:
+    _permission: 'administer url_embed'
Index: url_embed.services.yml
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/url_embed.services.yml b/url_embed.services.yml
--- a/url_embed.services.yml	(revision c3469227d337723507b5d1409e2a483efb7daadf)
+++ b/url_embed.services.yml	(revision 515020552861edaf2f104b03eb7db26f9276ef21)
@@ -1,4 +1,4 @@
 services:
   url_embed:
     class: Drupal\url_embed\UrlEmbed
-    arguments: ['@cache.data', '@datetime.time', '@config.factory']
+    arguments: ['@cache.data', '@datetime.time', '@?config.factory', ['config']]