MDL-66151 Performance: Session Manager modularisation

Storage of session metadata has moved into the session handler class.
This allows for other classes to fully control session handling and
removes the dependancy on the core sessions database table.

Previously, the standard method of interaction with the
session metadata was direct DB calls; this may break other plugins as there
are now proper APIs available through the session manager.

Co-authored-by: Darren Cocco <[email protected]>
Co-authored-by: Trisha Milan <[email protected]>
Co-authored-by: Andrew Nicols <[email protected]>

lib/classes/plugininfo/auth.php

@@ -87,6 +87,7 @@ class auth extends base {
             $new = implode(',', array_flip($plugins));
             add_to_config_log('auth', $CFG->auth, $new, 'core');
             set_config('auth', $new);
+            \core\session\manager::destroy_by_auth_plugin($pluginname);
             // Remove stale sessions.
             \core\session\manager::gc();
             // Reset caches.
@@ -160,6 +161,7 @@ class auth extends base {
             $value = implode(',', $auths);
             add_to_config_log('auth', $CFG->auth, $value, 'core');
             set_config('auth', $value);
+            \core\session\manager::destroy_by_auth_plugin($this->name);
         }
 
         if (!empty($CFG->registerauth) and $CFG->registerauth === $this->name) {