MDL-65818 Security: Encryption API and admin setting for secure data

lib/adminlib.php

@@ -2724,6 +2724,58 @@ class admin_setting_configpasswordunmask_with_advanced extends admin_setting_con
     }
 }
 
+/**
+ * Admin setting class for encrypted values using secure encryption.
+ *
+ * @copyright 2019 The Open University
+ * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class admin_setting_encryptedpassword extends admin_setting {
+
+    /**
+     * Constructor. Same as parent except that the default value is always an empty string.
+     *
+     * @param string $name Internal name used in config table
+     * @param string $visiblename Name shown on form
+     * @param string $description Description that appears below field
+     */
+    public function __construct(string $name, string $visiblename, string $description) {
+        parent::__construct($name, $visiblename, $description, '');
+    }
+
+    public function get_setting() {
+        return $this->config_read($this->name);
+    }
+
+    public function write_setting($data) {
+        $data = trim($data);
+        if ($data === '') {
+            // Value can really be set to nothing.
+            $savedata = '';
+        } else {
+            // Encrypt value before saving it.
+            $savedata = \core\encryption::encrypt($data);
+        }
+        return ($this->config_write($this->name, $savedata) ? '' : get_string('errorsetting', 'admin'));
+    }
+
+    public function output_html($data, $query='') {
+        global $OUTPUT;
+
+        $default = $this->get_defaultsetting();
+        $context = (object) [
+            'id' => $this->get_id(),
+            'name' => $this->get_full_name(),
+            'set' => $data !== '',
+            'novalue' => $this->get_setting() === null
+        ];
+        $element = $OUTPUT->render_from_template('core_admin/setting_encryptedpassword', $context);
+
+        return format_admin_setting($this, $this->visiblename, $element, $this->description,
+                true, '', $default, $query);
+    }
+}
+
 /**
  * Empty setting used to allow flags (advanced) on settings that can have no sensible default.
  * Note: Only advanced makes sense right now - locked does not.