Sharepoint calendar overlay: The HTTP request is unauthorized with client authentication scheme 'Ntlm'.

Question

When I add an outlook web app url to add an overlaid calendar, I also have to add an Exchange server url or it throws an error. If I do that, the calendar itself then has this error:
The HTTP request is unauthorized with client authentication scheme 'Ntlm'. The authentication header received from the server was 'Bearer client_id="0000000xxx00", trusted_issuers="000000xxx00@*", token_types="app_asserted_user_v1 service_asserted_app_v1", authorization_uri="https://login.windows.net/common/oauth2/authorize"'. (14dxxxxx75b)

It shouldn't be this hard to display an owa calendar. Why has Msft struggled with this basic process for so many years? And if overlaying Exchange online calendars is still not supported, why is that option even present in the overlay settings? Makes no sense and is very misleading.

Answer 1

Hi @matt howell

Are you using SharePoint online?

SharePoint Online Doesn't support Calendar overlay with Exchange web service.

If you are using SharePoint on-premise, then this feature seems also to be limited.

It’s not supported to use Calendar overlay feature in SharePoint on-premise to retrieve from Exchange Online.

We can only overlay your own Exchange calendar. Since the Exchange calendar overlay works with the account credentials of the user who is current logged on. SharePoint uses the account information of the current user to retrieve calendar data from the Exchange Web Service.

This seems to be a known issue, and someone has reported this situation in user voice. Judging from the reply from SharePoint user voice admin, there seems to be no other workaround for this situation.

https://sharepoint.uservoice.com/forums/329214-sites-and-collaboration/suggestions/12298926-fix-the-ablility-to-overlay-an-exchange-calendar-o

Thank you for your understanding.

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Answer 2

"SharePoint Online Doesn't support Calendar overlay with Exchange web service."
So why is it provided as an option?