negotiate: treat attr-config equal to ldap-configuration

In the ldap-code, search.attributes can be either a string (single attribute) or an array of attributes... The negotiate attr-setting is equal to search.attributes, but was handled differently (as merely a string)

modules/negotiate/lib/Auth/Source/Negotiate.php

@@ -24,7 +24,7 @@ class Negotiate extends \SimpleSAML\Auth\Source
     protected $timeout = 30;
     protected $keytab = '';
     protected $base = array();
-    protected $attr = 'uid';
+    protected $attr = array('uid');
     protected $subnet = null;
     protected $admin_user = null;
     protected $admin_pw = null;
@@ -62,7 +62,7 @@ class Negotiate extends \SimpleSAML\Auth\Source
         $this->timeout = $config->getInteger('timeout', 30);
         $this->keytab = $config->getString('keytab');
         $this->base = $config->getArrayizeString('base');
-        $this->attr = $config->getString('attr', 'uid');
+        $this->attr = $config->getArrayizeString('attr', 'uid');
         $this->subnet = $config->getArray('subnet', null);
         $this->admin_user = $config->getString('adminUser', null);
         $this->admin_pw = $config->getString('adminPassword', null);