More targeted parameter stripping.

- Resolves VUFIND-1020.

module/VuFind/src/VuFind/Controller/MyResearchController.php

@@ -248,8 +248,14 @@ class MyResearchController extends AbstractBase
                 $logoutTarget = $this->getServerUrl('home');
             }
 
-            // clear querystring parameters
-            $logoutTarget = preg_replace('/\?.*/', '', $logoutTarget);
+            // If there is an auth_method parameter in the query, we should strip
+            // it out. Otherwise, the user may get stuck in an infinite loop of
+            // logging out and getting logged back in when using environment-based
+            // authentication methods like Shibboleth.
+            $logoutTarget = preg_replace(
+                '/([?&])auth_method=[^&]*&?/', '$1', $logoutTarget
+            );
+            $logoutTarget = rtrim($logoutTarget, '?');
         }
 
         return $this->redirect()