Error when opening Office docs using Microsoft Connector

[Kathy Dickason]

We have Confluence Data Center 7.20.1 running on a Linux server.  

I have turned on Office Connector (disabling the Companion App).

I see the option to Edit in Word when viewing an attachment.  

When I click the Edit in Word option for a file, Word fires up and attempts to open the document, but it throws this Microsoft Word error, "Sorry, we couldn't open 'https://confluence.myservername.gov/servlet/confluence/editinword/85262678/attachments/ocauth/f-bunchofcharacters-/filename.docx. "   Then there is just an OK button.  No other information is provided.  

We are using Microsoft Office Professional Plus 2016 on desktops.  This same thing happens with PPT and Excel files. 

NOTE:  There are no special characters in the filename.  It is simply file.docx 

[Kathy Dickason]

So more info:  The Microsoft applications are prompting users for a certificate and defaulting to a cert called "Communications Server".   If users don't change that, the error comes up.  But if we have users click the More choices on the Cert screen, then select their PKI cert, they can edit the doc in Word as expected.  I'm not sure why users are being prompted for a cert, I'd like to turn this off if anyone knows where I might do that!