OAuth2: Authenticate Users with Google

OAuth2 is the industry-standard protocol for authorization. It provides a mechanism for users to grant web and desktop applications access to private information without sharing their username, password and other private credentials.

This tutorial builds an extension that accesses a user's Google contacts using the Google People API and the Chrome Identity API. Because extensions don’t load over HTTPS, can’t perform redirects or set cookies, they rely on the Chrome Identity API to use OAuth2.

Get Started

Begin by creating a directory and the following starter files.

The full, completed extension can be downloaded here.

manifest.json

Add the manifest by creating a file called manifest.json and include the following code. Or download the file here.

  {
    "name": "OAuth Tutorial FriendBlock",
    "version": "1.0",
    "description": "Uses OAuth to connect to Google's People API and display contacts photos.",
    "manifest_version": 2,
    "browser_action": {
      "default_title": "FriendBlock, friends face's in a block."
    },
    "background": {
      "scripts": [
        "background.js"
      ],
      "persistent": false
    }
  }

background.js

Add the background script by creating a file called background.js and include the following code. Or download the file here.

  chrome.browserAction.onClicked.addListener(function() {
    chrome.tabs.create({url: 'index.html'});
  });

index.html

Add an HTML file called index.html and include the following code. Or download the file here.

  <html>
    <head>
      <title>FriendBlock</title>
      <style>
        button {
          padding: 10px;
          background-color: #3C79F8;
          display: inline-block;
        }
      </style>
    </head>
    <body>
      <button>FriendBlock Contacts</button>
      <div id="friendDiv"></div>
    </body>
  </html>

Upload to the Developer Dashboard

Package the extension directory into a .zip file and upload it to the Chrome Developer Dashboard without publishing it:

  1. At the Developer Dashboard, click Add new item.
  2. Click Choose file and select the .zip extension directory and upload it.
  3. Without filling in additional fields, select Save Draft and return to dashboard.

Find the extension under Your Listings and click on more info. From the popup, copy the public key and add it to the manifest inside the unzipped directory under the "key" field.

  {
    "name": "OAuth Tutorial FaceBlcok",
  ...
    "key": "ThisKeyIsGoingToBeVeryLong/go8GGC2u3UD9WI3MkmBgyiDPP2OreImEQhPvwpliioUMJmERZK3zPAx72z8MDvGp7Fx7ZlzuZpL4yyp4zXBI+MUhFGoqEh32oYnm4qkS4JpjWva5Ktn4YpAWxd4pSCVs8I4MZms20+yx5OlnlmWQEwQiiIwPPwG1e1jRw0Ak5duPpE3uysVGZXkGhC5FyOFM+oVXwc1kMqrrKnQiMJ3lgh59LjkX4z1cDNX3MomyUMJ+I+DaWC2VdHggB74BNANSd+zkPQeNKg3o7FetlDJya1bk8ofdNBARxHFMBtMXu/ONfCT3Q2kCY9gZDRktmNRiHG/1cXhkIcN1RWrbsCkwIDAQAB"
  }

Compare IDs

Open the Extensions Management page at chrome://extensions, ensure developer mode is enabled and upload the unpackaged extension directory. Compare the extension ID on the extensions management page to the Item ID in the Developer Dashboard. They should match.

The ID of the extension matches in all places.

The extension will maintain the same ID by including the "key" field in the manifest. Preserving a single ID is essential for API registration.

Create OAuth Client ID

Navigate to the Google API console and create a new project. Once ready, select Credentials in the sidebar, click Create credentials and choose OAuth client ID.

Create credentials for extension.

On the Create client ID page, select Chrome App. Fill out the name of the extension and place the extension ID at the end of the URL in the Application ID field.

Fill out extension information.

Finish by clicking create. The console will provide an OAuth client ID.

Register OAuth in Manifest

Include the "oauth2" field in the extension manifest. Place the generated OAuth client ID under "client_id". Include an empty string in "scopes" for now.

{
  "name": "OAuth Tutorial FriendBlock",
  ...
  "oauth2": {
    "client_id": "yourExtensionOAuthClientIDWillGoHere.apps.googleusercontent.com",
    "scopes":[""]
  },
  ...
}

Initiate First OAuth Flow

Register the identity permission in the manifest.

  {
    "name": "OAuth Tutorial FaceBlcok",
    ...
    "permissions": [
      "identity"
    ],
    ...
  }

Create a file to manage the OAuth flow called oauth.js and include the following code. Or download it here.

  window.onload = function() {
    document.querySelector('button').addEventListener('click', function() {
      chrome.identity.getAuthToken({interactive: true}, function(token) {
        console.log(token);
      });
    });
  };

Place a script tag for oauth.js in the head of index.html.

  ...
    <head>
      <title>FriendBlock</title>
      ...
      <script type="text/javascript" src="oauth.js"></script>
    </head>
  ...

Reload the extension and click on the browser icon to open index.html. Open the console and click on the "FriendBlock Contacts" button. An OAuth token will appear in the console.

View the token in the console.

Enable the Google People API

Return to the Google API console and select Library from the sidebar. Search for "Google People API", click on the correct result and enable it.

Enable the People API.

Add the Google People API client libary to "scopes" in the extension manifest.

{
  "name": "OAuth Tutorial FaceBlcok",
  ...
  "oauth2": {
    "client_id": "yourExtensionOAuthClientIDWillGoHere.apps.googleusercontent.com",
    "scopes": [
      "https://www.googleapis.com/auth/contacts.readonly"
    ]
  },
  ...
}

Return to the Google API console and navigate back to credentials. Click "Create credentials" and select "API key" from the dropdown.

Create People API credentials.

Keep the generated API key for later use.

Create First API Request

Now that the extension has proper permissions, credentials, and can authorize a Google user, it can request data through the People API. Update the code in oauth.js to match below.

  window.onload = function() {
    document.querySelector('button').addEventListener('click', function() {
      chrome.identity.getAuthToken({interactive: true}, function(token) {
        let init = {
          method: 'GET',
          async: true,
          headers: {
            Authorization: 'Bearer ' + token,
            'Content-Type': 'application/json'
          },
          'contentType': 'json'
        };
        fetch(
            'https://people.googleapis.com/v1/contactGroups/all?maxMembers=20&key=<API_Key_Here>',
            init)
            .then((response) => response.json())
            .then(function(data) {
              console.log(data)
            });
      });
    });
  };

Replace <API_Key_Here> with the API key generated from the Google API console. The extension should log a JSON object that includes an array of people/account_ids under the memberResourceNames field.

Block Faces

Now that the extension is returning a list of the user's contacts, it can make additional requests to retrieve those contact's profiles and information . The extension will use the memberResourceNames to retrieve the photo information of user contacts. Update oauth.js to include the following code.

  window.onload = function() {
    document.querySelector('button').addEventListener('click', function() {
      chrome.identity.getAuthToken({interactive: true}, function(token) {
        let init = {
          method: 'GET',
          async: true,
          headers: {
            Authorization: 'Bearer ' + token,
            'Content-Type': 'application/json'
          },
          'contentType': 'json'
        };
        fetch(
            'https://people.googleapis.com/v1/contactGroups/all?maxMembers=20&key=<API_Key_Here>',
            init)
            .then((response) => response.json())
            .then(function(data) {
              let photoDiv = document.querySelector('#friendDiv');
              let returnedContacts = data.memberResourceNames;
              for (let i = 0; i < returnedContacts.length; i++) {
                fetch(
                    'https://people.googleapis.com/v1/' + returnedContacts[i] +
                        '?personFields=photos&key=<API_Key_Here>',
                    init)
                    .then((response) => response.json())
                    .then(function(data) {
                      let profileImg = document.createElement('img');
                      profileImg.src = data.photos[0].url;
                      photoDiv.appendChild(profileImg);
                    });
              };
            });
      });
    });
  };

Reload and return to the extension. Click the FriendBlock button and ta-da! Enjoy contact's faces in a block.

Contact faces in a block.