public function getClient($key)
    {
        if (!isset($this->serviceMap[$key])) {
            throw new \InvalidArgumentException(sprintf(
                'There is no OAuth2 client called "%s". Available are: %s',
                $key,
                implode(', ', array_keys($this->serviceMap))
            ));
        }

        return $this->container->get($this->serviceMap[$key]);
    }