Update Claims values in ASP.NET One Core

I have to SignOutAsync and SignInAsync again in order to update the cookie?

Answer is yes.

Easiest way is you can manually sign-out and sign-in (create claims again) inside the same action method where you are updating the email.

The best solution is to save this into a classic session?

I suggest not to do that. Using session state explicitly is a bad practice in ASP.Net MVC.

Another option, instead of SignOutAsync and SignInAsync, is to use RefreshSignInAsync.

Example:

var user = await _userManager.FindByIdAsync(yourId);
await _signInManager.RefreshSignInAsync(user);

View the RefreshSignInAsync code in the SignInManager (net 5.0.8): https://github.com/dotnet/aspnetcore/blob/ae2eabad0e49302d0632a7dde917fdc68d960dc4/src/Identity/Core/src/SignInManager.cs#L170