Make HTTP middleware easier to use

server/settings/admin/settings.go

Index: server/settings/admin/settings.go
diff --git a/server/settings/admin/settings.go b/server/settings/admin/settings.go
index c6aed6509a277ab929d795bd1b8a086f810bc0ae..ac0061a8210f27ef06d7ae99fdc8061704e6a685 100644
--- a/server/settings/admin/settings.go
+++ b/server/settings/admin/settings.go
@@ -5,20 +5,21 @@
 package admin
 
 import (
 	"net/http"
 
 	"github.com/julienschmidt/httprouter"
 	"golang.org/x/net/context"
 
 	"github.com/luci/luci-go/server/auth"
 	"github.com/luci/luci-go/server/auth/xsrf"
+	"github.com/luci/luci-go/server/router"
 	"github.com/luci/luci-go/server/settings"
 	"github.com/luci/luci-go/server/templates"
 )
 
 type fieldWithValue struct {
 	settings.UIField
 	Value string
 }
 
 type validationError struct {
@@ -37,21 +38,23 @@ func withPage(c context.Context, rw http.ResponseWriter, p httprouter.Params, cb
 		templates.MustRender(c, rw, "pages/error.html", templates.Args{
 			"Error": "No such settings",
 		})
 		return
 	}
 	if err := cb(id, page); err != nil {
 		replyError(c, rw, err)
 	}
 }
 
-func settingsPageGET(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
+func settingsPageGET(ctx *router.Context) {
+	c, rw, p := ctx.Context, ctx.Writer, ctx.Params
+
 	withPage(c, rw, p, func(id string, page settings.UIPage) error {
 		title, err := page.Title(c)
 		if err != nil {
 			return err
 		}
 		overview, err := page.Overview(c)
 		if err != nil {
 			return err
 		}
 		fields, err := page.Fields(c)
@@ -75,21 +78,23 @@ func settingsPageGET(c context.Context, rw http.ResponseWriter, r *http.Request,
 			"ID":             id,
 			"Title":          title,
 			"Overview":       overview,
 			"Fields":         withValues,
 			"XsrfTokenField": xsrf.TokenField(c),
 		})
 		return nil
 	})
 }
 
-func settingsPagePOST(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
+func settingsPagePOST(ctx *router.Context) {
+	c, rw, r, p := ctx.Context, ctx.Writer, ctx.Request, ctx.Params
+
 	withPage(c, rw, p, func(id string, page settings.UIPage) error {
 		title, err := page.Title(c)
 		if err != nil {
 			return err
 		}
 		fields, err := page.Fields(c)
 		if err != nil {
 			return err
 		}