fix(jwt): log decode errors for better debugging

Added error logging to capture JWT decode exceptions, aiding in pinpointing issues during authentication. This change improves troubleshooting and enhances the overall robustness of the JWT handling process.

classes/core_jwt_manager.php

@@ -99,6 +99,7 @@ class core_jwt_manager
         try {
             $decoded = JWT::decode($keyvalue, new Key($secret, 'HS256'));
         } catch (\Exception $e) {
+            error_log('JWT decode error: ' . $e->getMessage());
             throw new \moodle_exception('invalidkey');
         }