code: public function updateCredentials($user, $password)
      {
          $oldUser = $this->credentials->getUsername();
          $this->credentials = new Credentials($this->credentials->getClientId(), $user, $password);
          unset($password);
          if ($this->client instanceof Client) {
              $this->client = $this->oauth2Middleware = null;
              $this->client = $this->getClient();
          }
          if ($this->cache instanceof CacheProvider) {
              $this->cache->setNamespace(md5($this->basepath . $this->credentials->getUsername() . $this->credentials->getPassword()));
          }
          $this->logger->notice('Updated user!', ['old' => $oldUser, 'new' => $user]);
      }
docs: Changes the credentials used to authenticate with QBank.
  
  Changing the credentials will effectively switch the user using QBank and is useful when implementing some tiered
  service.
  
  @param string $user     username of the new user
  @param string $password password of the new user