diff --git a/badges/backpack-connect.php b/badges/backpack-connect.php
index ff77f490ee5..0dceb336a8a 100644
--- a/badges/backpack-connect.php
+++ b/badges/backpack-connect.php
@@ -43,6 +43,10 @@ if ($persistedissuer) {
     $returnurl = new moodle_url('/badges/backpack-connect.php',
         ['action' => 'authorization', 'sesskey' => sesskey(), 'backpackid' => $backpackid]);
 
+    // If scope is not passed as parameter, use the issuer supported scopes.
+    if (empty($scope)) {
+        $scope = $issuer->get('scopessupported');
+    }
     $client = new core_badges\oauth2\client($issuer, $returnurl, $scope, $externalbackpack);
     if ($client) {
         if (!$client->is_logged_in()) {
diff --git a/badges/classes/oauth2/client.php b/badges/classes/oauth2/client.php
index 575985b796d..8e635bcec03 100644
--- a/badges/classes/oauth2/client.php
+++ b/badges/classes/oauth2/client.php
@@ -222,6 +222,7 @@ class client extends \core\oauth2\client {
         $callbackurl = self::callback_url();
 
         if ($granttype == 'authorization_code') {
+            $this->basicauth = true;
             $params = array('code' => $code,
                 'grant_type' => $granttype,
                 'redirect_uri' => $callbackurl->out(false),
@@ -236,7 +237,7 @@ class client extends \core\oauth2\client {
             );
         }
         if ($this->basicauth) {
-            $idsecret = urlencode($this->clientid) . ':' . urlencode($this->clientsecret);
+            $idsecret = $this->clientid . ':' . $this->clientsecret;
             $this->setHeader('Authorization: Basic ' . base64_encode($idsecret));
         } else {
             $params['client_id'] = $this->clientid;
@@ -244,11 +245,13 @@ class client extends \core\oauth2\client {
         }
         // Requests can either use http GET or POST.
         $response = $this->post($this->token_url(), $this->build_post_data($params));
-        $r = json_decode($response);
         if ($this->info['http_code'] !== 200) {
-            throw new moodle_exception('Could not upgrade oauth token');
+            $debuginfo = !empty($this->error) ? $this->error : $response;
+            throw new moodle_exception('oauth2refreshtokenerror', 'core_error', '', $this->info['http_code'], $debuginfo);
         }
 
+        $r = json_decode($response);
+
         if (is_null($r)) {
             throw new moodle_exception("Could not decode JSON token response");
         }