I have a user that’s having trouble signing in to our Office 365 tenant in Safari or the macOS Office apps. When they use Chrome, they authenticate and get the Duo prompt just fine. When they try and get to one of our Shibboleth protected sites in Chrome, they get the duo prompt just fine. However, if they try to sign in to the Office desktop apps or portal.office.com using Safari, they complete the Azure username/password screens just fine, but instead of getting the Duo prompt, they immediately get a “500: Internal Server Error”.
It’s almost like Safari has no trouble reaching Duo, unless it’s Azure that’s directing Safari to contact Duo.