public function getAccessToken()
    {
        return $this->requestHandler->sendRequestAsync('POST', 'api/v4/oauth/access_token/')->then(
            function ($tokenValues) {
                parse_str($tokenValues, $tokenArray);
                $token = $tokenArray['oauth_token'];
                $tokenSecret = $tokenArray['oauth_token_secret'];
                $this->requestHandler->setAccessTokenCredentials($token, $tokenSecret);
                return $tokenArray;
            }
        );
    }