We have a reverse proxy that does SAML authentication and then translates it to kerberos delegation to our SharePoint Server Subscription Edition web app with Windows Integrated authentication. This works fine for browsing the web interface.
But how do we open files in Word for example? Right now, Word will open the URL to the file, but display the login page from ADFS instead of the document content. It is not a login prompt, it just opens the login page's HTML in the editor.