CSOM - Get GUID of Web that Permissions are Inherited From

I am backing up web permissions of a company's SharePoint Online Sites (1000+)

Some site collections have up to 10 levels from sub sites. 

I am currently capturing  the web ID and parent web ID.

I would also like to capture the web ID of the web that permissions are inherited from.  Meaning, a web could inherit permissions from any higher level parent web (Could be the parent web or grand-parent web or great-grand-parent, etc).

Thanks,
tjk

TJK