chrome.identity User Authentication in a Chrome Extension

Question

I\'m trying to write a chrome extension that requires user authentication.
Google\'s tutorial suggests that I need to upload to the web store first to get a key:

Answer 1

A bit late, but here is the source of my earlier confusion

It is a bit counterintuitive, but immediately after beginning a chrome extension / app, you have to 'publish' on the web store to obtain a consistent key and ID. If you are using the Chrome Dev Editor, hit the upper-left hamburger menu and click "Publish to the Chrome Web Store".

Once it finishes, you can then click "Open the developer dashboard" and save your app as a draft. Then you will see your full list of published apps and click 'more info' next to your app and copy the key between -----BEGIN PUBLIC KEY----- and -----END PUBLIC KEY-----. Paste that into your manifest as"key" and you can move on to develop offline.

Answer 2

You don't have to upload an extension to the Chrome Web Store in order to use the chrome.identity API. It suffices to have a valid extension ID. The easiest way to get started is to copy the 32-character extension ID from chrome://extensions/ to your project's credentials section at the API console ^{see screenshot below}.
Though if you ever want to publish the extension or use it in a different profile or computer, then you'd better choose an extension ID that you control. This can be done by setting the "key" key in the manifest file. See Obtaining Chrome Extension ID for development for a detailed answer on generating these keys.

For example, try out the following extension, using a key that I just generated. It will print your user info in a dialog.

manifest.json

{
    "key": "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA0W0/YVPvLrj2cWBOXfPBBYwPp56R+OJb9QLudyMpigF+V4DFV0NEUnbo9iA6m+7cVPiD6YbhbIaiAoHSdtqEKwaYvrEJRGuGsLjDq+RMwG2x+FcGIsO4ny0BuZaZ/Q2+DaL33NBUl2h9dIi1xa0Suq6qpoJ4yykTu9y7Q6rB9ulJze6DiZL7LWU5NzHCEWt21zAhpLZOqvYY8wzY69pMf+P0+uOLuy87x84rvCRNegbSmEYLC5f4y6ikjVnFUxJBxMlpMg3bByxbrLVBFPuHj4khkr6adUXgks2vBBHFcrRh5EYXopI+PLwUJPfFtzyN8+L7swen9kcK8gXMwX28KwIDAQAB",
    "name": "Identity test",
    "version": "1",
    "manifest_version": 2,
    "background": {
        "scripts": ["background.js"]
    },  
    "permissions": [
        "identity"
    ],  
    "oauth2": {
        "client_id": "1014705257182-52ffffdl9dbiec2ln22stokphlaq0v7gor.apps.googleusercontent.com",
        "scopes": ["profile"]   
    }   
}

background.js

chrome.identity.getAuthToken({
    interactive: true
}, function(token) {
    if (chrome.runtime.lastError) {
        alert(chrome.runtime.lastError.message);
        return;
    }
    var x = new XMLHttpRequest();
    x.open('GET', 'https://www.googleapis.com/oauth2/v2/userinfo?alt=json&access_token=' + token);
    x.onload = function() {
        alert(x.response);
    };
    x.send();
});