How do you open a ClosedXML Workbook from a stream?

I have an ASP.NET MVC app where a user can upload an xlsx file to be processed.

This creates a HttpPostedFileBase object in the upload that has a handy stream method, HttpPostedFileBase.InputStream.

I want to process the file using ClosedXML, but I don't know how to construct a XLWorkbook object from a stream. Other SO answers use a normal file like this:

 string fileName = "C:\\Folder1\\Prev.xlsx";
 var workbook = new XLWorkbook(fileName);

This question explores how to SaveAs as stream, but I want to create from a stream.

So how do you open a XLWorkbook from a stream?