Gorilla mux implementation for this example https://twitter.com/tebeka/status/1597506203218718721

main.go

package main

import (
	"context"
	"fmt"
	"net/http"

	"github.com/google/uuid"
	"github.com/gorilla/mux"
)

type CtxKeyType int

const IDCtxKey CtxKeyType = 3

// https://twitter.com/tebeka/status/1597506203218718721

func main() {
	r := mux.NewRouter()
	r.Use(func(h http.Handler) http.Handler {
		fn := func(w http.ResponseWriter, r *http.Request) {
			id := uuid.NewString()
			ctx := context.WithValue(r.Context(), IDCtxKey, id)
			r = r.Clone(ctx)

			h.ServeHTTP(w, r)
		}
		return http.HandlerFunc(fn)
	})
	r.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		rid := r.Context().Value(IDCtxKey)
		fmt.Fprintf(w, "ID: %v\n", rid)
	})
	http.ListenAndServe(":8080", r)
}