code: protected function getPasswordEncoder($userData = null)
      {
          if (isset($userData['encoder']) && is_string($userData['encoder'])) {
              $name = $userData['encoder'];
          } else {
              $name = $this->config["encoder"];
          }
  
          $container = $this->picoAuth->getContainer();
          
          if (!$container->has($name)) {
              throw new \RuntimeException("Specified LocalAuth encoder is not resolvable.");
          }
  
          return $container->get($name);
      }
docs: Returns encoder instance for the specified user
  
  If the user data array is not specified, returns the default
  encoder instance.
  
  @param null|array $userData User data array
  @return \PicoAuth\Security\Password\Encoder\PasswordEncoderInterface
  @throws \RuntimeException If the encoder is not resolvable