Request extensions (a feature of the `http` crate, not specifically hyper/warp/axum) are "just" a typemap, which is "just" a HashMap where keys are TypeIDs rath

Request extensions (a feature of the `http` crate, not specifically hyper/warp/axum) are "just" a typemap, which is "just" a HashMap where keys are TypeIDs rather than strings. It's slightly less footgunny than something like Go's Context, although I still dislike it because checking for the presence of something happens at runtime only, so if you're messing with middleware composition, it's still too easy to accidentally get it wrong.