Why? 🤷

We needed a much simpler and extensively documented way to add "Sign-in with Google" capability to our Elixir App(s).

What? 💭

An Elixir package that seamlessly handles Google OAuth2 Authentication/Authorization in as few steps as possible.
Following best practices for security & privacy and avoiding complexity by having sensible defaults for all settings.

We built a lightweight solution that only does one thing and is easy for complete beginners to understand/use.
There were already several available options for adding Google Auth to apps on hex.pm/packages?search=google
that all added far too many implementation steps (complexity) and had incomplete docs (@doc false) and tests.
e.g: github.com/googleapis/elixir-google-api which is a "generated" client and is considered "experimental".
We have drawn inspiration from several sources including code from other programming languages to build this package. This result is much simpler than anything else and has both step-by-step instructions and a complete working example App including how to encrypt tokens for secure storage to help you ship your app fast.

Who? 👥

This module is for people building apps using Elixir/Phoenix who want to ship the "Sign-in with Google" feature faster and more maintainably.

It's targetted at complete beginners with no prior experience/knowledge of auth "schemes" or "strategies".
Just follow the detailed instructions and you'll be up-and running in 5 minutes.

How? ✅

You can add Google Authentication to your Elixir App using elixir_auth_google
in under 5 minutes by following these 5 easy steps:

1. Add the hex package to deps 📦

Open your project's mix.exs file and locate the deps (dependencies) section.
Add a line for :elixir_auth_google in the deps list:

def deps do
  [
    {:elixir_auth_google, "~> 1.6.9"}
  ]
end

Once you have added the line to your mix.exs, remember to run the mix deps.get command in your terminal to download the dependencies.

2. Create Google APIs Application OAuth2 Credentials 🆕

Create a Google Application if you don't already have one, generate the OAuth2 Credentials for the application and save the credentials as environment variables accessible by your app, or put them in your config file.

Note: There are a few steps for creating a set of Google APIs credentials, so if you don't already have a Google App, we created the following step-by-step guide to make it quick and relatively painless: create-google-app-guide.md
Don't be intimidated by all the buzz-words; it's quite straightforward. And if you get stuck, ask for help!

3. Setup CLIENT_ID and CLIENT_SECRET in your project

You may either add those keys as environment variables or put them in the config:

export GOOGLE_CLIENT_ID=631770888008-6n0oruvsm16kbkqg6u76p5cv5kfkcekt.apps.googleusercontent.com
export GOOGLE_CLIENT_SECRET=MHxv6-RGF5nheXnxh1b0LNDq

Or add the following in the config file:

config :elixir_auth_google,
  client_id: "631770888008-6n0oruvsm16kbkqg6u76p5cv5kfkcekt.apps.googleusercontent.com",
  client_secret: "MHxv6-RGF5nheXnxh1b0LNDq"

⚠️ Don't worry, these keys aren't valid. They are just here for illustration purposes.

4. Create a GoogleAuthController in your Project 📝

Create a new file called lib/app_web/controllers/google_auth_controller.ex and add the following code:

defmodule AppWeb.GoogleAuthController do
  use AppWeb, :controller

  @doc """
  `index/2` handles the callback from Google Auth API redirect.
  """
  def index(conn, %{"code" => code}) do
    {:ok, token} = ElixirAuthGoogle.get_token(code, MyAppWeb.Endpoint.url())
    {:ok, profile} = ElixirAuthGoogle.get_user_profile(token.access_token)
    conn
    |> put_view(AppWeb.PageView)
    |> render(:welcome, profile: profile)
  end
end

This code does 3 things:

• Create a one-time auth token based on the response code sent by Google after the person authenticates.
• Request the person's profile data from Google based on the access_token
• Render a :welcome view displaying some profile data to confirm that login with Google was successful.

5. Create the /auth/google/callback Endpoint 📍

Open your router.ex file and locate the section that looks like scope "/", AppWeb do

Add the following line:

get "/auth/google/callback", GoogleAuthController, :index

Sample: lib/app_web/router.ex#L20

Different callback url?

You can specify the env var

export GOOGLE_CALLBACK_PATH=/myauth/google_callback

or add it in the configuration

Or add the following in the config file:

config :elixir_auth_google,
  # ...
  callback_path: "/myauth/google_callback"

6. Add the "Login with Google" Button to your Template ✨

In order to display the "Sign-in with Google" button in the UI, we need to generate the URL for the button in the relevant controller, and pass it to the template.

Open the lib/app_web/controllers/page_controller.ex file and update the index function:

From:

def index(conn, _params) do
  render(conn, "index.html")
end

To:

def index(conn, _params) do
  oauth_google_url = ElixirAuthGoogle.generate_oauth_url(conn)
  render(conn, "index.html",[oauth_google_url: oauth_google_url])
end

You can add extra features the the generated url by passing the state as a string, or any other query as a map of key/value pairs.

oauth_google_url = ElixirAuthGoogle.generate_oauth_url(conn, state)

Will result in Google Sign In link with &state=state added. And something like:

oauth_google_url = ElixirAuthGoogle.generate_oauth_url(conn, %{lang: 'pt-BR'})

Will return a url with lang=pt-BR included in the sign in request.

Alternatively pass the url of your App into generate_oauth_url/1

We have noticed that on fly.io where the Phoenix App is proxied, passing the conn struct to ElixirAuthGoogle.generate_oauth_url/2 is not effective. See dwyl/elixir-auth-google/issues/94

So we added an alternative way of invoking generate_oauth_url/2 passing in the url of your App:

def index(conn, _params) do
  base_url = MyAppWeb.Endpoint.url()
  oauth_google_url = ElixirAuthGoogle.generate_oauth_url(base_url)
  render(conn, "index.html",[oauth_google_url: oauth_google_url])
end

This uses Phoenix.Endpoint.url/0 which is available in any Phoenix App.

Just remember to replace MyAppWeb with the name of your App. 😉

6.1 Update the page/index.html.eex Template

Open the /lib/app_web/templates/page/index.html.eex file and type the following code:

<section class="phx-hero">
  <h1>Welcome to Awesome App!</h1>
  <p>To get started, login to your Google Account: <p>
  <a href={@oauth_google_url}>
    <img src="https://i.imgur.com/Kagbzkq.png" alt="Sign in with Google" />
  </a>
</section>

Done! 🚀

The home page of the app now has a big "Sign in with Google" button:

When the person clicks the button, and authenticates with their Google Account, they will be returned to your App where you can display a "login success" message:

Optional: Scopes

Most of the time you will only want/need the person's email address and profile data when authenticating with your App. In the cases where you need more specific access to a Google service, you will need to specify the exact scopes. See: https://developers.google.com/identity/protocols/oauth2/scopes

Once you know the scope(s) your App needs access to, simply define them using an environment variable, e.g:

GOOGLE_SCOPE="email contacts photoslibrary"

Those double-quotes (") encapsulating the environment variable String are important. Without them your system will only assign the first word to the GOOGLE_SCOPE. e.g: email and ignore the remaining scopes you need. or you can set them as a config variable if you prefer:

config :elixir_auth_google,
  :google_scope: "email contacts photoslibrary"

With that configured, your App will gain access to the requested services once the person authenticates/authorizes.

Optimised SVG+CSS Button

In step 6.1 above, we suggest using an <img> for the Sign in with GitHub button.

But even though this image appears small 389 × 93 px https://i.imgur.com/Kagbzkq.png it is "only" 8kb:

We could spend some time in a graphics editor optimising the image, but we know we can do better by using our CSS skills! 💡

Note: This is the official button provided by Google: developers.google.com/identity/images/signin-assets.zip
So if there was any optimisation they could squeeze out of it, they probably would have done it before publishing the zip!

The following code re-creates the <img> using the GitHub logo SVG and CSS for layout/style:

<div style="display:flex; flex-direction:column; width:368px; margin-left:133px;">
  <link href="https://fonts.googleapis.com/css?family=Roboto&display=swap">

  <a href="<%= @oauth_google_url %>"
    style="display:inline-flex; align-items:center; min-height:50px;
      background-color:#4285F4; font-family:'Roboto',sans-serif;
      font-size:28px; color:white; text-decoration:none;
      margin-top: 12px">
      <div style="background-color: white; margin:2px; padding-top:18px; padding-bottom:6px; min-height:59px; width:72px">
      <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 533.5 544.3"
        width="52px" height="35" style="display:inline-flex; align-items:center;" >
        <path d="M533.5 278.4c0-18.5-1.5-37.1-4.7-55.3H272.1v104.8h147c-6.1 33.8-25.7 63.7-54.4 82.7v68h87.7c51.5-47.4 81.1-117.4 81.1-200.2z" fill="#4285f4"/>
        <path d="M272.1 544.3c73.4 0 135.3-24.1 180.4-65.7l-87.7-68c-24.4 16.6-55.9 26-92.6 26-71 0-131.2-47.9-152.8-112.3H28.9v70.1c46.2 91.9 140.3 149.9 243.2 149.9z" fill="#34a853"/>
        <path d="M119.3 324.3c-11.4-33.8-11.4-70.4 0-104.2V150H28.9c-38.6 76.9-38.6 167.5 0 244.4l90.4-70.1z" fill="#fbbc04"/>
        <path d="M272.1 107.7c38.8-.6 76.3 14 104.4 40.8l77.7-77.7C405 24.6 339.7-.8 272.1 0 169.2 0 75.1 58 28.9 150l90.4 70.1c21.5-64.5 81.8-112.4 152.8-112.4z" fill="#ea4335"/>
      </svg>
    </div>
    <div style="margin-left: 27px;">
      Sign in with Google
    </div>
  </a>
</div>

We created this from scratch using the SVG of the Google logo and some basic CSS.
For the "making of" journey see: #25

The result looks better than the <img> button:

It can be scaled to any screen size so it will always look great!
Using http://bytesizematters.com we see that our SVG+CSS button is only 1kb:

That is an 87.5% bandwidth saving on the 8kb of the .png button. And what's more it reduces the number of HTTP requests which means the page loads even faster.

This is used in the Demo app: lib/app_web/templates/page/index.html.eex

i18n

The biggest advantage of having an SVG+CSS button is that you can translate the button text!
Since the text/copy of the button is now just text in standard HTML, the user's web browser can automatically translate it!
e.g: French 🇬🇧 > 🇫🇷

This is much better UX for the 80% of people in the world who do not speak English fluently. The single biggest engine for growth in startup companies is translating their user interface into more languages. Obviously don't focus on translations while you're building your MVP, but if it's no extra work to use this SVG+CSS button and it means the person's web browser can automatically localise your App!

Accessibility

The SVG+CSS button is more accessible than the image. Even thought the <img> had an alt attribute which is a lot better than nothing, the SVG+CSS button can be re-interpreted by a non-screen device and more easily transformed.

Even More Detail 💡

If you want to dive a bit deeper into understanding how this package works, You can read and grok the code in under 10 minutes: /lib/elixir_auth_google.ex

We created a basic demo Phoenix App, to show you exactly how you can implement the elixir_auth_google package: https://github.com/dwyl/elixir-auth-google-demo It's deployed to Heroku: https://elixir-auth-google-demo.herokuapp.com
(no data is saved so you can play with it - and try to break it!)

And if you want/need a more complete real-world example including creating sessions and saving profile data to a database, take a look at our MVP: https://github.com/dwyl/app-mvp-phoenix

Notes 📝

• Official Docs for Google Identity Platform: https://developers.google.com/identity/choose-auth
  • Web specific sample code (JS): https://developers.google.com/identity/sign-in/web
• Google Sign-In for server-side apps: https://developers.google.com/identity/sign-in/web/server-side-flow
• Using OAuth 2.0 for Web Server Applications: https://developers.google.com/identity/protocols/OAuth2WebServer
• Google Auth Branding Guidelines: https://developers.google.com/identity/branding-guidelines
  Only two colors are permitted for the button: white #FFFFFF and blue #4285F4

Fun Facts 📈📊

Unlike other "social media" companies, Google/Alphabet does not report it's Monthly Active Users (MAUs) or Daily Active Users (DAUs) however they do release stats in drips in their Google IO or YouTube events. The following is a quick list of facts that make adding Google Auth to your App a compelling business case:

• As of May 2019, there are over 2.5 Billion active Android devices; 87% global market share. All these people have Google Accounts in order to use Google services.
• YouTube has 2 billion monthly active YouTube users (signed in with a Google Account).
• Gmail has 1.5 Billion monthly active users a 27% share of the global email client market.
• 65% of Small and Medium sized businesses use Google Apps for business.
• 90%+ of startups use Gmail. This is a good proxy for "early adopters".
• 68% of schools in the US use Google Classroom and related G-suite products.
  So the next generation of internet/app users have Google accounts.
• Google has 90.46% of the search engine market share worldwide. 95.4% on Mobile.

Of the 4.5 billion internet users (58% of the world population), around 3.2 billion (72%) have a Google account. 90%+ of tech "early adopters" use Google Apps which means that adding Google OAuth Sign-in is the logical choice for most Apps.

Privacy Concerns? 🔐

A common misconception is that adding Google Auth Sign-in sends a user's application data to Google. This is false and App developers have 100% control over what data is sent to (stored by) Google. An App can use Google Auth to authenticate a person (identify them and get read-only access to their personal details like first name and email address) without sending any data to Google. Yes, it will mean that Google "knows" that the person is using your App, but it will not give Google any insight into how they are using it or what types of data they are storing in the App. Privacy is maintained. So if you use the @dwyl app to plan your wedding or next holiday, Google will not have any of that data and will not serve any annoying ads based on your project/plans.