/**
  * @return string
  */
 private function getAuthHeader()
 {
     if ($this->accessToken === null) {
         throw new AuthenticationException(0, "Access token not set");
     }
     return 'Bearer ' . $this->accessToken->getAccessToken();
 }
 /**
  * @param AccessToken $accessToken
  */
 public function saveAccessToken(AccessToken $accessToken)
 {
     file_put_contents($this->filePath . '/' . $this->fileName, $accessToken->toJson());
 }