Issue Summary

Since 9.2 end users are experiencing authentication prompts in external calendar clients such as MS Outlook desktop app and the Apple Calendar desktop app relating to calendars belonging to Confluence's Team Calendar, of which they have subscribed to. 

Environment:

• Confluence 9.2+
• Apple Calendar app, and Outlook Calendar app in Windows. 

Steps to Reproduce

1. Create a Team Calendar with a few events
2. Generate a Subscription URL under (…) > Subscribe
3. In the “Subscribe to Calendar” prompt, choose “Microsoft Outlook (browser)“ as Calendar App
4. Copy the generated link.
5. In your Calendar app, click on File > New Calendar Subscription
6. Enter the .ics URL and click on Subscribe. Check the Auto-refresh to “Every 45 minutes”
7. Now, you can see that the calendar events will be retrieved from Confluence and added to your Calendar app.

Expected Results

End users don't get prompted for authentication in future synchronisations with the Calendar

Actual Results

End users get prompted for authentication. If you authenticate, it works for some time but you will be prompted again after some time. 

Looking at the Confluence access logs, we see the following during the Calendar subscription moment: 

xxx.50.0.2 - [09/Jun/2025:08:27:13 +0000] "GET /confluence/rest/calendar-services/1.0/calendar/export/subcalendar/private/136ad4e7eea081ed518bff7156d8faf88905499d.ics HTTP/1.1" 200 2166 112 /confluence/rest/calendar-services/1.0/calendar/export/subcalendar/private/136ad4e7eea081ed518bff7156d8faf88905499d.ics http-nio-8090-exec-8 "macOS/15.5 (24F74) dataaccessd/1.0" xxx.50.0.2 xxx.50.0.5 8815FB101C9616A9B4A78A869F8C5EAF -  

xxx.50.0.2 - [09/Jun/2025:08:27:19 +0000] "GET /confluence/rest/calendar-services/1.0/calendar/export/subcalendar/private/136ad4e7eea081ed518bff7156d8faf88905499d.ics HTTP/1.1" 200 2166 116 /confluence/rest/calendar-services/1.0/calendar/export/subcalendar/private/136ad4e7eea081ed518bff7156d8faf88905499d.ics http-nio-8090-exec-9 "macOS/15.5 (24F74) dataaccessd/1.0"  xxx.50.0.2 xxx.50.0.5 8815FB101C9616A9B4A78A869F8C5EAF JSESSIONID=8815FB101C9616A9B4A78A869F8C5EAF   

Notice that the value of the “User session ID“ (%S) in the first request returns a session ID with value 8815FB101C9616A9B4A78A869F8C5EAF; and the cookie JSESSIONID is not set. However, in the second request, the JSESSIONID is set while retrieving the Calendar events.

The session ID received in the first request is used for the Calendar app as JSESSIONID value. If you wait 45 minutes till the next synchronisation from the Apple Calendar, you will see an error in the app with a  warning () symbol close to the calendar name. If you click on the Calendar, the following prompt for authentication appears (in Apple Calendar): 

Reviewing once more the Confluence access logs, we can see that the SessionID is now null, while the JSESSIONID sent by the Calendar App remains as the previous value. This triggers a 401 Unauthorized because the SessionID expired after 1 minute with the configuration we set in the beginning. 

xxx.50.0.2 - [09/Jun/2025:08:33:05 +0000] "GET /confluence/rest/calendar-services/1.0/calendar/export/subcalendar/private/136ad4e7eea081ed518bff7156d8faf88905499d.ics HTTP/1.1" 401 770 7 /confluence/rest/calendar-services/1.0/calendar/export/subcalendar/private/136ad4e7eea081ed518bff7156d8faf88905499d.ics http-nio-8090-exec-3 "macOS/15.5 (24F74) dataaccessd/1.0"  xxx.50.0.2 xxx.50.0.5 - JSESSIONID=8815FB101C9616A9B4A78A869F8C5EAF 

Workaround

Workaround 1) 

In the Calendar subscription url, add os_authType=none parameter. Hence, if your Calendar URL is: 

/rest/calendar-services/1.0/calendar/export/subcalendar/private/136ad4e7eea081ed518bff7156d8faf88905499d.ics 

, it should look like this:

/rest/calendar-services/1.0/calendar/export/subcalendar/private/136ad4e7eea081ed518bff7156d8faf88905499d.ics?os_authType=none 

(Only for MS Outlook) Workaround 2) 

As an alternative, you could subscribe to your Calendar URL using Outlook Web App (OWA), as described in the Microsoft KB article You can't add an Internet calendar in Outlook 2019, Outlook 2016, and Outlook for Microsoft 365