If this is information that's independent of the request (that is, something used in a variety of requests) and is used to control the processing of the request, then I'm more likely to put the data ...

These headers are passed along with the request or the response. The Save-Data header is a “client hint” request header that is available in Chrome and Opera web browsers.

Pass parameters via request header in ASP.NET Core MVC The request header is yet another option for passing parameters to your action methods.