if there is no `upn` claim for a user easy auth breaks

[paule96]

There is a rare case where a JWT token doesn't contain a upn claim.
Then easy auth will fail with a NullReferenceException.

How this can happen?

If you have a user that is not part of you AAD as a member but is a guest he doesn't get a upn

Where do we explode?

CZ.AspNetCore.EasyAuthAuthentication/src/CZ.AspNetCore.EasyAuthAuthentication/Services/EasyAuthForAuthorizationTokenService.cs

Line 91 in 2be5ffd

xMsClientPrincipal["upn"]?.ToString() ?? string.Empty : // this appends if an user is using the auth token from the /.auth/me site on the website