Adds tests in demo app for service worker compatibility with Firebase Auth (#571)

* Adds tests in demo app for service worker compatibility with Firebase Auth.

This modifies the service worker to append the ID token in every fetch
request via a custom HTTP header.

Using Functions with Hosting, an HTTP endpoint was setup which will
parse the ID token from the header and verify it using Admin SDK and
then return a status response.

A button is added to the demo app to test this. When a user is signed
in, the user's uid is returned, otherwise an error is shown.

* [AUTOMATED]: License Headers

* Fixes comment.

* Renames /echoIdToken endpoint to /checkIfAuthenticated.

Author: bojeil-google

packages/auth/.gitignore

@@ -16,3 +16,4 @@ dist/
 # Local config.
 **/.firebaserc
 demo/public/config.js
+demo/functions/node_modules/

packages/auth/buildtools/run_demo.sh

@@ -34,4 +34,4 @@ cp ../firebase/firebase-auth.js demo/public/dist/firebase-auth.js
 cp ../firebase/firebase-database.js demo/public/dist/firebase-database.js
 # Serve demo app.
 cd demo
-`yarn bin`/firebase serve
+`yarn bin`/firebase serve --only hosting,functions

packages/auth/demo/firebase.json

@@ -6,8 +6,8 @@
     "public": "public",
     "rewrites": [
       {
-        "source": "**",
-        "destination": "/index.html"
+        "source": "/checkIfAuthenticated",
+        "function": "checkIfAuthenticated"
       }
     ]
   }

packages/auth/demo/functions/index.js

@@ -0,0 +1,42 @@
+/**
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * @fileoverview Defines the HTTP endpoints hosted via firebase functions which
+ * are used to test service worker functionality for Firebase Auth via demo
+ * app.
+ */
+
+const functions = require('firebase-functions');
+const admin = require('firebase-admin');
+
+admin.initializeApp(functions.config().firebase);
+
+exports.checkIfAuthenticated = functions.https.onRequest((req, res) => {
+  const idToken = req.get('x-id-token');
+  res.setHeader('Content-Type', 'application/json');
+  if (idToken) {
+    admin.auth().verifyIdToken(idToken)
+        .then((decodedIdToken) => {
+          res.status(200).send(JSON.stringify({uid: decodedIdToken.sub}));
+        })
+        .catch((error) => {
+          res.status(400).send(JSON.stringify({error: error.code}));
+        });
+  } else {
+    res.status(403).send(JSON.stringify({error: 'Unauthorized access'}));
+  }
+});