Added sample for handling CORS requests.

.gitignore

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 .nyc_output
 yarn.lock
 package-lock.json
+.DS_Store

functions/cors/README.md

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+<img src="https://avatars2.githubusercontent.com/u/2810941?v=3&s=96" alt="Google Cloud Platform logo" title="Google Cloud Platform" align="right" height="96" width="96"/>
+
+# Google Cloud Functions - CORS (Cross-Origin Resource Sharing) sample
+
+See:
+
+* [Cloud Functions CORS tutorial][tutorial]
+* [Cloud Functions CORS sample source code][code]
+
+[tutorial]: https://cloud.google.com/functions/docs/writing/http#handling_cors_requests
+[code]: index.js
+
+## Deploy and run the sample
+
+See the [Cloud Functions CORS tutorial][tutorial].
+
+## Run the tests
+
+1. Read and follow the [prerequisites](../../#how-to-run-the-tests).
+
+2. Install dependencies:
+
+        npm install
+
+3. Run the tests:
+
+        npm test

functions/cors/index.js

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+/**
+ * Copyright 2018, Google, LLC.
+ * 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.
+ */
+
+'use strict';
+
+// [START functions_cors]
+exports.corsEnabledFunction = (req, res) => {
+  // Set CORS headers for preflight requests
+  // e.g. allow GETs from any origin with the Content-Type header
+  // and cache preflight response for an 3600s
+  res.set('Access-Control-Allow-Origin', '*');
+  res.set('Access-Control-Allow-Methods', 'GET');
+  res.set('Access-Control-Allow-Headers', 'Content-Type');
+  res.set('Access-Control-Max-Age', '3600');
+
+  // Send response to OPTIONS requests and terminate the function execution
+  if (req.method === 'OPTIONS') {
+    res.status(204).send('');
+  }
+
+  // Set CORS headers for the main request
+  res.removeHeader('Access-Control-Allow-Methods');
+  res.removeHeader('Access-Control-Allow-Headers');
+  res.removeHeader('Access-Control-Max-Age');
+
+  res.send('Hello World!');
+};
+// [END functions_cors]
+
+// [START functions_cors_auth]
+exports.corsEnabledFunctionAuth = (req, res) => {
+  // Set CORS headers for preflight requests
+  // allows GETS from origin https://mydomain.com with Authorization header
+  res.set('Access-Control-Allow-Origin', 'https://mydomain.com');
+  res.set('Access-Control-Allow-Methods', 'GET');
+  res.set('Access-Control-Allow-Headers', 'Authorization');
+  res.set('Access-Control-Allow-Credentials', 'true');
+  res.set('Access-Control-Max-Age', '3600');
+
+  // Send response to OPTIONS requests and terminate the function execution
+  if (req.method === 'OPTIONS') {
+    res.status(204).send('');
+  }
+
+  res.removeHeader('Access-Control-Allow-Methods');
+  res.removeHeader('Access-Control-Allow-Headers');
+  res.removeHeader('Access-Control-Max-Age');
+
+  res.send('Hello World!');
+};
+// [END functions_cors_auth]

functions/cors/package.json

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+{
+  "name": "nodejs-docs-samples-functions-cors",
+  "version": "0.0.1",
+  "private": true,
+  "license": "Apache-2.0",
+  "author": "Google Inc.",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/GoogleCloudPlatform/nodejs-docs-samples.git"
+  },
+  "engines": {
+    "node": ">=4.3.2"
+  },
+  "scripts": {
+    "lint": "repo-tools lint",
+    "pretest": "npm run lint",
+    "test": "ava -T 20s --verbose test/*.test.js"
+  },
+  "dependencies": {},
+  "devDependencies": {
+    "@google-cloud/nodejs-repo-tools": "2.2.1",
+    "ava": "0.25.0",
+    "semistandard": "^12.0.1",
+    "sinon": "4.4.2"
+  },
+  "cloud-repo-tools": {
+    "requiresKeyFile": true,
+    "requiresProjectId": true
+  }
+}

functions/cors/test/index.test.js

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+/**
+ * Copyright 2018, Google, LLC.
+ * 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.
+ */
+
+'use strict';
+
+const sinon = require(`sinon`);
+const test = require(`ava`);
+const functions = require(`../`);
+
+function getMocks () {
+  const mainReq = {
+    method: 'GET'
+  };
+
+  const preflightReq = {
+    method: 'OPTIONS'
+  };
+
+  const res = {
+    set: sinon.stub(),
+    removeHeader: sinon.stub(),
+    send: sinon.stub().returnsThis(),
+    status: sinon.stub().returnsThis()
+  };
+
+  return {
+    mainReq: mainReq,
+    preflightReq: preflightReq,
+    res: res
+  };
+}
+
+test.serial(`should respond to preflight request (no auth)`, (t) => {
+  const mocks = getMocks();
+
+  functions.corsEnabledFunction(mocks.preflightReq, mocks.res);
+
+  t.true(mocks.res.status.calledOnceWith(204));
+  t.true(mocks.res.send.called);
+});
+
+test.serial(`should respond to main request (no auth)`, (t) => {
+  const mocks = getMocks();
+
+  functions.corsEnabledFunction(mocks.mainReq, mocks.res);
+
+  t.true(mocks.res.send.calledOnceWith(`Hello World!`));
+});
+
+test.serial(`should respond to preflight request (auth)`, (t) => {
+  const mocks = getMocks();
+
+  functions.corsEnabledFunctionAuth(mocks.preflightReq, mocks.res);
+
+  t.true(mocks.res.status.calledOnceWith(204));
+  t.true(mocks.res.send.called);
+});
+
+test.serial(`should respond to main request (auth)`, (t) => {
+  const mocks = getMocks();
+
+  functions.corsEnabledFunctionAuth(mocks.mainReq, mocks.res);
+
+  t.true(mocks.res.send.calledOnceWith(`Hello World!`));
+});