Implement interface to serialize exceptions to JSON-API format

Related to #118

src/Core/Exceptions/PermissionDeniedException.php

@@ -12,6 +12,26 @@ namespace Flarum\Core\Exceptions;
 
 use Exception;
 
-class PermissionDeniedException extends Exception
+class PermissionDeniedException extends Exception implements JsonApiSerializable
 {
+    /**
+     * Return the HTTP status code to be used for this exception.
+     *
+     * @return int
+     */
+    public function getStatusCode()
+    {
+        return 401;
+    }
+
+    /**
+     * Return an array of errors, formatted as JSON-API error objects.
+     *
+     * @see http://jsonapi.org/format/#error-objects
+     * @return array
+     */
+    public function getErrors()
+    {
+        return [];
+    }
 }