public function validateAccessToken($accessToken)
    {
        $result = DB::table('oauth_session_access_tokens')
                    ->select('oauth_session_access_tokens.session_id as session_id',
                            'oauth_sessions.client_id as client_id',
                            'oauth_clients.secret as client_secret',
                            'oauth_sessions.owner_id as owner_id',
                            'oauth_sessions.owner_type as owner_type')
                    ->join('oauth_sessions', 'oauth_session_access_tokens.session_id', '=', 'oauth_sessions.id')
                    ->join('oauth_clients', 'oauth_sessions.client_id', '=', 'oauth_clients.id')
                    ->where('access_token', $accessToken)
                    ->where('access_token_expires', '>=', time())
                    ->first();

        return (is_null($result)) ? false : (array) $result;
    }