dotnet run --project MangledHeaders
Navigate to http://localhost:5000 to observe the manglage or lack thereof.
Uncomment .Use(async (context, next) => await next.Invoke())
in Startup.cs and try again.
Targets ASP.NET Core 3.0. To try 2.2 or 3.1, comment-out the target framework and header propagation package reference in MangledHeaders.csproj, and uncomment the corresponding other ones.