reverseproxy: Set origreq in active health check (#5284)

* reverseproxy: Set origreq in active health check

Fix #5281

* Oops; dereference Request

modules/caddyhttp/reverseproxy/healthchecks.go

@@ -266,7 +266,8 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, upstre
 		u.Host = net.JoinHostPort(host, portStr)
 	}
 
-	// attach dialing information to this request
+	// attach dialing information to this request, as well as context values that
+	// may be expected by handlers of this request
 	ctx := h.ctx.Context
 	ctx = context.WithValue(ctx, caddy.ReplacerCtxKey, caddy.NewReplacer())
 	ctx = context.WithValue(ctx, caddyhttp.VarsCtxKey, map[string]any{
@@ -276,6 +277,8 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, upstre
 	if err != nil {
 		return fmt.Errorf("making request: %v", err)
 	}
+	ctx = context.WithValue(ctx, caddyhttp.OriginalRequestCtxKey, *req)
+	req = req.WithContext(ctx)
 	for key, hdrs := range h.HealthChecks.Active.Headers {
 		if strings.ToLower(key) == "host" {
 			req.Host = h.HealthChecks.Active.Headers.Get(key)