Why did user.identity.name case sensitivity change in c#?

Question

So I am working with a .NET Core app v1.0 in C#, it uses windows authentication.

Last time I used it on 14/02/2017. But today (16/02/2017) it stopped working properly because User.Identity.Name started to return case sensitive user name from MS Active Directory. So it went from "DOMAIN\jdoe" to "DOMAIN\JDoe" in the span of 1 day.

What possible reasons could make it suddenly change?

Answer 1

I believe the reason has to do with Active Directory changes rather than something in your code.

At any case, it's best practice to allways upper or lower case you usernames:

User.Identity.Name.ToLower();
User.Identity.Name.ToUpper();