In order to get SharePoint integration to work, an application must be registered in Office 365

The system can only use certificate for authentication.

Create a self-signed certificate with PowerShell on the server.

Upload the certificate to the application in Office 365 Admin center.

Make sure the app permissions is set with the following access

Ensure that the certificate has a private key when exporting.

Make sure permission on the server is granted for the private keys, the certificate needs to be added to the person store

If you receive this error "Possible cause: this may be a known issue with apps build against .NET Desktop 4.6 or lower. Either target a higher version of .NET desktop - 4.6.1 and above, or use a different certificate type (non-CNG) or sign your own assertion as described at" But the app is built with .net 4.8"

Then the user does not have permission to the certificate