Cro is a general Raku framework for parallel processing, and it has an HTTP client and server with Cro::HTTP. As it is written by Jonathan Worthington, it would be my first port of call. Searching further for HTTP, that site also shows HTTP::Client, which maybe is more focused on an HTTP client.

As you want to write a small CGI, searching for HTTP also returns HTTP::Easy, which claims to be PSGI-compatible. This is likely the closest thing you'll get for writing CGI-like scripts.

Personally, I would look into Cro, as it seems to have both, HTTP support and session support.