You may like Hurl [1]: it's an Open source cli based on curl (libcurl to be exact), to run and test HTTP requests with plain text (I'm one of the maintainers). We recently add --curl option to come back to curl. Give it a shout!
I've recently used Hurl to create a test suite for migrating a complex Nginx configuration to Caddy and it was a great choice!
I ran Caddy replacing the upstreams with mockbin-like services (don't remember which one I used) so it would respond with information about the request made by the proxy, so Hurl could make assertions on that.
Recently tried out hurl for a project to show how abstract tests can be run in a specific environment. Great tool, it will definitely stay as part of my standard toolset.
[1]: https://hurl.dev