HttpRequest.Params doesn't return the values like framework did

The only incompatibility still now is that Params apparently returns a combined collection of QueryString, Form, Cookies, and ServerVariables items. Unlike the indexer, which returns the first item found from those collections.
I'm unsure how I can accomplish that in an efficient way.

_Originally posted by @sdekock in https://github.com/dotnet/systemweb-adapters/issues/310#issuecomment-1479776444_