This is based on a feature prototype in Razor pages. Essentially properties annotated with TempData attribute are round-tripped for a single request. Some cleverness is required to determine if the value of the property was changed to determine if it needs to be stashed again in TempData (https://github.com/aspnet/RazorPages/blob/master/src/Microsoft.AspNetCore.Mvc.RazorPages/TempDataPropertyTracker.cs).