config_service: Add authentication to the UI.

appengine/config_service/ui/src/config-ui/front-page.html

 <!--
   Copyright 2017 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.
 -->
 
 <link rel="import" href="../../bower_components/app-layout/app-layout.html">
 <link rel="import" href="../../bower_components/iron-ajax/iron-ajax.html">
 <link rel="import" href="../../bower_components/paper-button/paper-button.html">
 <link rel="import" href="../../bower_components/paper-search/paper-search-bar.html">
@@ skipping 22 matching lines @@
         height: 100%;
         margin: auto;
       }
     </style>
 
     <iron-ajax
         auto
         id="requestConfigs"
         url="/_ah/api/config/v1/config-sets"
         handle-as="json"
-        on-response="_onGotConfigSets">
+        on-response="_onGotConfigSets"
+        headers="[[auth_headers]]">
     </iron-ajax>
     
     <div class="search-bar">
       <paper-search-bar query="{{query}}"></paper-search-bar>
     </div>
     
     <div class="config-list">
       <template is="dom-if" if="[[isLoading]]">
         <div class="center">Fetching config sets...</div>
       </template>
@@ skipping 54 matching lines @@
         this.searchResults = this.configSetList.filter(e => e.config_set.includes(this.query));
       },
 
       _handleClick: function(event) {
         window.location = window.location.href + event.model.config.config_set;
       },
 
     });
   </script>
 </dom-module>