Issue #1798734 by Berdir, ACF, leschekfm, heyrocker, alexpott: Convert drupal_private_key() to the configuration system.

core/includes/common.inc

@@ -4814,9 +4814,9 @@ function drupal_get_hash_salt() {
  *   The private key.
  */
 function drupal_get_private_key() {
-  if (!($key = variable_get('drupal_private_key', 0))) {
+  if (!($key = state()->get('system.private_key'))) {
     $key = drupal_hash_base64(drupal_random_bytes(55));
-    variable_set('drupal_private_key', $key);
+    state()->set('system.private_key', $key);
   }
   return $key;
 }

core/includes/update.inc

@@ -400,6 +400,12 @@ function update_prepare_d8_bootstrap() {
       $theme_config->save();
       $disabled_themes->save();
 
+      // Migrate the private key to state. This is used to create the token for
+      // the upgrade batch so needs to be be done before the upgrade has begun.
+      update_variables_to_state(array(
+        'drupal_private_key' => 'system.private_key',
+      ));
+
       // Update the dynamic include paths that might be used before running the
       // proper update functions.
       update_prepare_stored_includes();

core/modules/system/lib/Drupal/system/Tests/Upgrade/StateSystemUpgradePathTest.php

@@ -59,6 +59,10 @@ class StateSystemUpgradePathTest extends UpgradePathTestBase {
       'value' => 'kdm95qppDDlyZrcUOx453YwQqDA4DNmxi4VQcxzFU9M',
       'variable_name' => 'cron_key',
     );
+    $expected_state['system.private_key'] = array(
+      'value' => 'G38mKqASKus8VGMkMzVuXImYbzspCQ1iRT2iEZpMYmQ',
+      'variable_name' => 'drupal_private_key',
+    );
     $expected_state['tracker.index_nid'] = array(
       'value' => 0,
       'variable_name' => 'tracker_index_nid',

core/modules/system/tests/upgrade/drupal-7.state.system.database.php

@@ -47,6 +47,10 @@ db_merge('variable')
   ->key(array('name' => 'cron_key'))
   ->fields(array('value' => serialize('kdm95qppDDlyZrcUOx453YwQqDA4DNmxi4VQcxzFU9M')))
   ->execute();
+db_merge('variable')
+  ->key(array('name' => 'drupal_private_key'))
+  ->fields(array('value' => serialize('G38mKqASKus8VGMkMzVuXImYbzspCQ1iRT2iEZpMYmQ')))
+  ->execute();
 db_merge('variable')
   ->key(array('name' => 'node_cron_comments_scale'))
   ->fields(array('value' => serialize(1.0 / 1000)))