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

examples/appengine/helloworld_flexible/frontend/main.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 main implements HTTP server that handles requests to default
 // module.
 package main
 
 import (
         "net/http"
@@ skipping 34 matching lines @@
                         "IsAdmin":     isAdmin,
                         "User":        auth.CurrentUser(c),
                         "LoginURL":    loginURL,
                         "LogoutURL":   logoutURL,
                 }, nil
         },
 }
 
 // base returns the root middleware chain.
 func base() router.MiddlewareChain {
-        methods := auth.Authenticator{
-                &server.OAuth2Method{Scopes: []string{server.EmailScope}},
-                server.CookieAuth,
-                &server.InboundAppIDAuthMethod{},
-        }
         return gaemiddleware.BaseProd().Extend(
                 templates.WithTemplates(templateBundle),
-                auth.Use(methods),
-                auth.Authenticate,
+                auth.Authenticate(&auth.Authenticator{
+                        Methods: []auth.Method{
+                                &server.OAuth2Method{Scopes: []string{server.EmailScope}},
+                                server.CookieAuth,
+                                &server.InboundAppIDAuthMethod{},
+                        },
+                }),
         )
 }
 
 //// Routes.
 
 func main() {
         r := router.New()
 
         gaemiddleware.InstallHandlers(r)
         r.GET("/", base(), indexPage)
         http.DefaultServeMux.Handle("/", r)
 
         appengine.Main()
 }
 
 //// Handlers.
 
 func indexPage(c *router.Context) {
         templates.MustRender(c.Context, c.Writer, "pages/index.html", nil)
 }