auth: Refactor how authentication methods are passed to server/auth library.

examples/appengine/helloworld_standard/frontend/handler.go

 // 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 frontend implements HTTP server that handles requests to default
 // module.
 package frontend
 
 import (
         "net/http"
@@ skipping 39 matching lines @@
                         "LoginURL":    loginURL,
                         "LogoutURL":   logoutURL,
                 }, nil
         },
 }
 
 // pageBase returns the middleware chain for page handlers.
 func pageBase() router.MiddlewareChain {
         return gaemiddleware.BaseProd().Extend(
                 templates.WithTemplates(templateBundle),
-                auth.Use(auth.Authenticator{server.CookieAuth}),
-                auth.Authenticate,
+                auth.Authenticate(server.CookieAuth),
         )
 }
 
 // prpcBase returns the middleware chain for pRPC API handlers.
 func prpcBase() router.MiddlewareChain {
         // OAuth 2.0 with email scope is registered as a default authenticator
         // by importing "github.com/luci/luci-go/appengine/gaeauth/server".
         // No need to setup an authenticator here.
         //
         // For authorization checks, we use per-service decorators; see
@@ skipping 35 matching lines @@
         api.InstallHandlers(r, prpcBase())
 
         http.DefaultServeMux.Handle("/", r)
 }
 
 //// Handlers.
 
 func indexPage(c *router.Context) {
         templates.MustRender(c.Context, c.Writer, "pages/index.html", nil)
 }