MDL-78132 badges: move apiBase consumption to backpack

The logic to create the issuer has been moved to the backpack form
in order to improve the workflow and update the apiBase with the
proper value comming from the badgeconnect.json manifest file.

So, as part of this change in the workflow, the following changes
has been also implemented (to make the UI easier for users):

- The "Open Badges" oAuth issuer button has been removed from the
"OAuth Services" admin page. As they are created/updated when a backpack
is saved, this button is not required anymore.
- The "OAuth2 services" and "Backpack API URL" parameters have been
removed from the Manage backpacks form, because they are created on
the fly each time the backpack is saved.

lib/badgeslib.php

@@ -798,6 +798,40 @@ function badges_delete_site_backpack($id) {
  */
 function badges_save_external_backpack(stdClass $data) {
     global $DB;
+    if ($data->apiversion == OPEN_BADGES_V2P1) {
+        // Check if there is an existing issuer for the given backpackapiurl.
+        foreach (core\oauth2\api::get_all_issuers() as $tmpissuer) {
+            if ($data->backpackweburl == $tmpissuer->get('baseurl')) {
+                $issuer = $tmpissuer;
+                break;
+            }
+        }
+
+        // Create the issuer if it doesn't exist yet.
+        if (empty($issuer)) {
+            $issuer = new \core\oauth2\issuer(0, (object) [
+                'name' => $data->backpackweburl,
+                'baseurl' => $data->backpackweburl,
+                // Note: This is required because the DB schema is broken and does not accept a null value when it should.
+                'image' => '',
+            ]);
+            $issuer->save();
+        }
+
+        // This can't be run from PHPUNIT because testing platforms need real URLs.
+        // In the future, this request can be moved to the moodle-exttests repository.
+        if (!PHPUNIT_TEST) {
+            // Create/update the endpoints for the issuer.
+            \core\oauth2\discovery\imsbadgeconnect::create_endpoints($issuer);
+            $data->oauth2_issuerid = $issuer->get('id');
+
+            $apibase = \core\oauth2\endpoint::get_record([
+                'issuerid' => $data->oauth2_issuerid,
+                'name' => 'apiBase',
+            ]);
+            $data->backpackapiurl = $apibase->get('url');
+        }
+    }
     $backpack = new stdClass();
 
     $backpack->apiversion = $data->apiversion;