code: protected function getEbayHeaders($operationName)
      {
          $credentials = $this->getConfig('credentials');
          $appId = $credentials->getAppId();
          $certId = $credentials->getCertId();
          $devId = $credentials->getDevId();
  
          $headers = [];
  
          // Add required headers first.
          $headers[self::HDR_API_VERSION] = $this->getConfig('apiVersion');
          $headers[self::HDR_OPERATION_NAME] = $operationName;
          $headers[self::HDR_SITE_ID] = $this->getConfig('siteId');
  
          // Add optional headers.
          if ($appId) {
              $headers[self::HDR_APP_ID] = $appId;
          }
  
          if ($certId) {
              $headers[self::HDR_CERT_ID] = $certId;
          }
  
          if ($devId) {
              $headers[self::HDR_DEV_ID] = $devId;
          }
  
          if ($this->getConfig('authorization')) {
              $headers[self::HDR_AUTHORIZATION] = $this->getConfig('authorization');
          }
  
          /**
           * Note that we have no way of detecting that the actual request has an attachment.
           */
          if ($operationName === 'UploadSiteHostedPictures') {
              $headers['Content-Type'] = 'multipart/form-data;boundary="boundary"';
          }
  
          return $headers;
      }
docs: Builds the needed eBay HTTP headers.
  
  @param string $operationName The name of the operation been called.
  
  @return array An associative array of eBay http headers.