1. 🔴 Redis::auth() called with 2 args — crashes every password-auth connection

  Queue/Backend/Redis.php:267
  $success = $this->redis->auth($this->password, $this->username);
  $this->redis is native phpredis (new \Redis()), whose auth() takes exactly one argument. I confirmed this live on this machine (PHP 8.3.30 / phpredis 6.3.0):
  Redis::auth() expects exactly 1 argument, 2 given  (ArgumentCountError)
  Because the second arg is always passed (username is null when unset), this throws for every existing user who uses a Redis password, not just ACL users — a hard regression on the
  plain redis backend. It also never actually transmits the ACL username. This path was clearly never exercised (the PR was tested against Sentinel, which uses the separate
  Credis_Client path). Fix:
  if ($success && !empty($this->password)) {
      $success = !empty($this->username)
          ? $this->redis->auth([$this->username, $this->password])
          : $this->redis->auth($this->password);
  }

  2. 🟠 RedisCluster backend silently drops the username

  Queue/Factory.php:87 calls setConfig($host, $port, $timeout, $password, $username) for all Redis backends, but Queue/Backend/RedisCluster.php:318 setConfig() still takes only 4
  params, and new \RedisCluster(...) (line 311) never receives a username. PHP silently ignores the extra userland arg (no crash), so a username configured in the UI has no effect and
  no error on the cluster backend — silent misconfiguration. Either add username support there or explicitly reject username + cluster.

  3. 🟡 New setting bypasses translations (project convention)

  SystemSettings.php:246,251 hardcodes English:
  $field->title = 'Redis Username';
  $field->inlineHelp = 'Username for Redis ACL authentication. Leave empty if not used.';
  Every sibling setting uses Piwik::translate('QueuedTracking_...') with keys in lang/en.json (e.g. createRedisPasswordSetting). Add
  QueuedTracking_RedisUsernameFieldTitle/...FieldHelp keys and use Piwik::translate. Minor: siblings also append . '</br>' to inlineHelp; this one doesn't.

  4. 🟡 No test coverage for the new path

  tests/Integration/Queue/Backend/RedisTest.php — nothing added for username, and the existing setConfig(...) calls still pass 4 args. A single ACL-auth integration test would have
  caught finding #1. Please add one.