On IIS (ANCM) : when a request contains a header such as foo:Québec, IIS decodes it as Qu�bec. (The "é" is replaced with codepoint U+FFFD). It is possible to enable Latin1 decoding using AppContext.SetSwitch("Microsoft.AspNetCore.Server.IIS.Latin1RequestHeaders", isEnabled: true); Please see: #22675

On Kestrel : when a request contains a header such as foo:Québec, Kestrel rejects it outright as 400.0 (Bad Request). It is possible to enable Latin1 decoding using KestrelServerOptions.RequestHeaderEncodingSelector property : https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.server.kestrel.core.kestrelserveroptions.requestheaderencodingselector?view=aspnetcore-5.0

However, on HttpSysServer, the option to enable Latin1 decoding is not present.

Describe the solution you'd like

An option to enable Latin1 request header decoding on HttpSysServer similar to Kestrel and IIS (ANCM)