code: protected function refreshToken(string $user): Slice
      {
          /**
           * @var $token Slice
           */
          $token = $this->tokens[$user];
  
          return $this->tokens[$user] = $this->authorize($user, [
              'grant_type'    => 'refresh_token',
              'refresh_token' => $token->getRequired('refresh_token'),
          ]);
      }
docs: @param string $user
  
  @return Slice
  
  @throws Invalid