Make HTTP middleware easier to use

appengine/logdog/coordinator/config/middleware.go

Index: appengine/logdog/coordinator/config/middleware.go
diff --git a/appengine/logdog/coordinator/config/middleware.go b/appengine/logdog/coordinator/config/middleware.go
index bef79ceb81eb25e0a01bd82e23f4f04587b2c900..de73495a95c4f700a70dfb9d6a1440ad95e1443b 100644
--- a/appengine/logdog/coordinator/config/middleware.go
+++ b/appengine/logdog/coordinator/config/middleware.go
@@ -1,28 +1,23 @@
 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package config
 
 import (
 	"net/http"
 
-	"github.com/julienschmidt/httprouter"
 	log "github.com/luci/luci-go/common/logging"
-	"github.com/luci/luci-go/server/middleware"
-	"golang.org/x/net/context"
+	"github.com/luci/luci-go/server/router"
 )
 
-// WithConfig is a middleware.Handler that installs the LogDog Coordinator
+// WithConfig is a middleware that installs the LogDog Coordinator
 // configuration into the Context.
-func WithConfig(h middleware.Handler) middleware.Handler {
-	return func(c context.Context, rw http.ResponseWriter, r *http.Request, params httprouter.Params) {
-		if err := UseConfig(&c); err != nil {
-			log.WithError(err).Errorf(c, "Failed to install service configuration.")
-
-			rw.WriteHeader(http.StatusInternalServerError)
-			return
-		}
-		h(c, rw, r, params)
+func WithConfig(c *router.Context, next router.Handler) {
+	if err := UseConfig(&c.Context); err != nil {
+		log.WithError(err).Errorf(c.Context, "Failed to install service configuration.")
+		c.Writer.WriteHeader(http.StatusInternalServerError)
+		return
 	}
+	next(c)
 }