When using Microsoft Office with a WebDAV share, Office programs
will prompt for authentication each time they are started, even if
the share is already mounted.

The only way to prevent all behavior implement Microsoft Office
Forms Based Authentication (OFBA) protocol.  This is what this
modules implements.

MS-OFBA is documented here
https://msdn.microsoft.com/en-us/library/office/cc313069%28v=office.12%29.aspx