Add exceptions from frontend

exceptions/generic/MDAccessDeniedException.php

@@ -0,0 +1,21 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Custom exception class for invalid page parameters.
+ */
+class MDAccessDeniedException extends Exception {
+
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        $errorMsg = 'Parameter: <b>' . $this->getMessage() . '</b> is not a valid, numeric values.';
+        return $errorMsg;
+
+    }
+
+}