Create Column in SharePoint to Store Salesforce ID

In SharePoint, for the desired Document Library, create a new column called SalesforceId. This column is required to enforce Salesforce sharing rules for record visibility. 

Configure sFiles to write to the SalesforceId column in SharePoint

1. From Salesforce Setup, navigate to: Custom Code | Custom Metadata Types.
2. Click Manage Records next to SharePoint Object Settings.
3. Find the object that you want to allow community users to see. For example, if it's on Account, click on the Edit next to Account's SharePoint Object Settings. 
4. Under Folder Custom Field Default Value, we will need to automatically set the Salesforce Id into the new Salesforceld SharePoint field we created. Add the following to the field:  

   SalesforceId:[Id]

   This tells sFiles to look for the SalesforceId column inside SharePoint and then sets the Salesforce object's Id whenever an upload occurs.
5. Click Save.

Set SalesforceId column in SharePoint for existing items

If you are configuring a net-new document library with no contents yet, you will not need to do anything here.  If the library already has files and folders that sFiles has created, you will need to set the SalesforceId field for any items in the library that you want to display in the context of the experience cloud.  This may be a time-consuming process if you have a large amount of existing files or folders.  It may be helpful to data-load or use SharePoint automation to set these values.  In order for sFiles to enforce Salesforce Sharing rules, the Salesforce record ID must be filled out to a Salesforce Record Id that corresponds to the record the experience user will use to access the file or folder.