public function scopeExists($scope, $client_id = null)
    {
        $scopes = explode(' ', $scope);
        if ($client_id) {
            // Get Client
            $client = $this->em->getRepository('OAuth2ServerBundle:Client')->find($client_id);

            if (!$client) {
                return false;
            }

            $valid_scopes = $client->getScopes();

            foreach ($scopes as $scope) {
                if (!in_array($scope, $valid_scopes)) {
                    return false;
                }
            }

            return true;
        }

        $valid_scopes = $this->sm->findScopesByScopes($scopes);

        return count($valid_scopes) == count($scopes);
    }