You have a SIEM that needs to analyze log files from Cloud SWG (aka WSS).
There is a REST API that can be used to integrate your SIEM with Cloud SWG.
Create the API Key on Cloud SWG portal
Implement the Sync API for Log Syncing
Once the API Key is generated, WSS provides the API method for the SIEM to download logs from the Cloud SWG. The SIEM tools need to pull those logs via HTTPS and with the configured API Key.
You need to involve your SIEM administrator to help you to consume the logs downloaded via SyncAPI. Symantec's technical support only provides the API Key and interface to download the logs.