New auth_get_auth_instance function, to get user's auth method

htdocs/auth/lib.php

@@ -399,6 +399,22 @@ function auth_get_auth_instances_for_institution($institution) {
     return $cache[$institution];
 }
 
+/**
+ * Given a user, returns the authentication instance used.
+ *
+ * @param  object   $user            User object with an authinstance member
+ * @return array                     Array of auth instance records
+ */
+function auth_get_auth_instance($user) {
+    static $cache = array();
+
+    if (!isset($cache[$user->id])) {
+        $cache[$user->id] = get_record('auth_instance', 'id', $user->authinstance, null, null, null, null, 'id, instancename, priority, authname');
+    }
+
+    return $cache[$user->id];
+}
+
 /**
  * Checks whether the current user needs to change their password, and handles
  * the password changing if it's required.