22. Google Authentication

Written by Tim Condon

In the previous chapters, you learned how to add authentication to the TIL web site. However, sometimes users don’t want to create extra accounts for an application and would prefer to use their existing accounts.

In this chapter, you’ll learn how to use OAuth 2.0 to delegate authentication to Google, so users can log in with their Google accounts instead.

OAuth 2.0

OAuth 2.0 is an authorization framework that allows third-party applications to access resources on behalf of a user. Whenever you log in to a website with your Google account, you’re using OAuth.

When you click Login with Google, Google is the site that authenticates you. You then authorize the application to have access to your Google data, such as your email. Once you’ve allowed the application access, Google gives the application a token. The app uses this token to authenticate requests to Google APIs. You’ll implement this technique in this chapter.

Note: You must have a Google account to complete this chapter. If you don’t have one, visit https://accounts.google.com/SignUp to create one.

Imperial

Writing all the necessary scaffolding to interact with Google’s OAuth system and get a token is a time-consuming job!

There’s a community package called Imperial, https://github.com/vapor-community/Imperial, that does the heavy lifting for you. It has integrations for Google, Facebook and GitHub with more planned.

Adding to your project

Open Package.swift in Xcode to add the new dependency. Replace .package(url: "https://github.com/vapor/auth.git", from: "2.0.0") with the following:

.package(url: "https://github.com/vapor/auth.git",
         from: "2.0.0"),
.package(url: "https://github.com/vapor-community/Imperial.git",
         from: "0.7.1")

Next, add the dependency to your App target’s dependency array, after "Authentication":

dependencies: ["FluentPostgreSQL",
               "Vapor",
               "Leaf",
               "Authentication",
               "Imperial"]

In Terminal, create a file for a new controller to manage Imperial’s routes:

touch Sources/App/Controllers/ImperialController.swift

Finally, in Terminal, regenerate the Xcode project to pull in the new dependency and include the new file:

vapor xcode -y

When the project opens in Xcode, open ImperialController.swift and create a new empty controller:

import Vapor
import Imperial
import Authentication

struct ImperialController: RouteCollection {
  func boot(router: Router) throws {

  }
}

This creates a new type, ImperialController, that conforms to RouteCollection, implementing the required boot(router:).

Open routes.swift and add the controller to your application at the bottom of routes(_:):

let imperialController = ImperialController()
try router.register(collection: imperialController)

Setting up your application with Google

To be able to use Google OAuth in your application, you must first register the application with Google. In your browser, go to https://console.developers.google.com/apis/credentials.

If this is the first time you’ve used Google’s credentials, the site prompts you to create a project:

Click Create to create a project for the TIL application. Fill in the form with an appropriate name, e.g. Vapor TIL:

After it creates the project, the site takes you back to the Google credentials page. This time, click Select and select the created project. Click Create Credentials to create credentials for the TIL app and choose OAuth client ID:

Next click Configure consent screen to set up the page Google presents to users, so they can allow your application access to their details.

Add a product name and click Save:

When creating a client ID, choose Web application. Add a redirect URI for your application for testing — http://localhost:8080/oauth/google. This is the URL that Google redirects back to once users have allowed your application access to their data.

If you want to deploy your application to the internet, such as with AWS or Heroku, add another redirect for the URL for that site — e.g., https://rw-til-vapor.herokuapp.com/oauth/google:

Click Create and the site gives you with your client ID and client secret:

Note: You must keep these safe and secure. Your secret allows you access to Google’s APIs, and you should not share or check the secret into source control. You should treat it like a password.

Setting up the integration

Now that you’ve registered your application with Google, you can start integrating Imperial. Open ImperialController.swift and add the following under boot(router:):

func processGoogleLogin(request: Request, token: String)
  throws -> Future<ResponseEncodable> {
    return request.future(request.redirect(to: "/"))
}

This defines a method to handle the Google login. The handler simply redirects the user to the home page — the same way that the regular login works. Imperial uses this method as the final callback once it has handled the Google redirect. Notice the use of request.future(_:) to create a future from request.redirect(to:), since the function that Imperial uses requires a Future.

Next, set up the Imperial routes by adding the following in boot(router:):

guard let googleCallbackURL =
  Environment.get("GOOGLE_CALLBACK_URL") else {
    fatalError("Google callback URL not set")
}
try router.oAuth(
  from: Google.self,
  authenticate: "login-google",
  callback: googleCallbackURL,
  scope: ["profile", "email"],
  completion: processGoogleLogin)

Here’s what this does:

• Get the callback URL for Google from an environment variable — this is the URL you set up in the Google console.
• Register Imperial’s Google OAuth router with your app’s router.
• Tell Imperial to use the Google handlers.
• Set up the /login-google route as the route that triggers the OAuth flow. This is the route the application uses to allow users to log in via Google.
• Provide the callback URL to Imperial.
• Request the profile and email scopes from Google — the application needs these to create a user.
• Set the completion handler to processGoogleLogin(request:token:) - the method you created above.

In order for Imperial to work, you need to provide it the client ID and client secret that Google gave you. You provide these to Imperial using environment variables. To do this in Xcode, click the Run scheme, then click Edit scheme:

Under the Arguments tab, add three new Environment Variables as shown below:

• GOOGLE_CALLBACK_URL: http://localhost:8080/oauth/google — this is the URL you provided to Google.
• GOOGLE_CLIENT_ID: The client ID provided by Google.
• GOOGLE_CLIENT_SECRET: The client secret provided by Google.

Integrating with web authentication

It’s important to provide a seamless experience for users and match the experience for the regular login. To do this, you need to create a new user when a user logs in with Google for the first time. To create a user, you can use Google’s API to get the necessary details using the OAuth token.

Sending requests to third-party APIs

At the bottom of ImperialController.swift, add a new type to decode the data from Google’s API:

struct GoogleUserInfo: Content {
  let email: String
  let name: String
}

The request to Google’s API returns many fields. However, you only care about the email, which becomes the username, and the name.

Next, under GoogleUserInfo, add the following:

extension Google {
  // 1
  static func getUser(on request: Request)
    throws -> Future<GoogleUserInfo> {
      // 2
      var headers = HTTPHeaders()
      headers.bearerAuthorization =
        try BearerAuthorization(token: request.accessToken())

      // 3
      let googleAPIURL =
        "https://www.googleapis.com/oauth2/v1/userinfo?alt=json"
      // 4
      return try request
        .client()
        .get(googleAPIURL, headers: headers)
        .map(to: GoogleUserInfo.self) { response in
        // 5
        guard response.http.status == .ok else {
          // 6
          if response.http.status == .unauthorized {
            throw Abort.redirect(to: "/login-google")
          } else {
            throw Abort(.internalServerError)
          }
        }
        // 7
        return try response.content
          .syncDecode(GoogleUserInfo.self)
      }
  }
}

Here’s what this does:

1. Add a new function to Imperial’s Google service that gets a user’s details from the Google API.
2. Set the headers for the request by adding the OAuth token to the authorization header.
3. Set the URL for the request — this is Google’s API to get the user’s information.
4. Use request.client() to create a client to send a request. get() sends an HTTP GET request to the URL provided. Unwrap the returned future response.
5. Ensure the response status is 200 OK.
6. Otherwise, return to the login page if the response was 401 Unauthorized or return an error.
7. Decode the data from the response to GoogleUserInfo and return the result.

Next, replace the contents of processGoogleLogin(request:token:) with the following:

// 1
return try Google
  .getUser(on: request)
  .flatMap(to: ResponseEncodable.self) { userInfo in
  // 2
  return User
    .query(on: request)
    .filter(\.username == userInfo.email)
    .first()
    .flatMap(to: ResponseEncodable.self) { foundUser in

    guard let existingUser = foundUser else {
      // 3
      let user = User(name: userInfo.name,
                      username: userInfo.email,
                      password: UUID().uuidString)
      // 4
      return user
        .save(on: request)
        .map(to: ResponseEncodable.self) { user in
        // 5
        try request.authenticateSession(user)
        return request.redirect(to: "/")
      }
    }
    // 6
    try request.authenticateSession(existingUser)
    return request.future(request.redirect(to: "/"))
  }
}

Here’s what the new code does:

1. Get the user information from Google.
2. See if the user exists in the database by looking up the email as the username.
3. If the user doesn’t exist, create a new User using the name and email from the user information from Google. Set the password to a UUID string, since you don’t need it. This ensures that no one can login to this account via a normal password login.
4. Save the user and unwrap the returned future.
5. Call request.authenticateSession(_:) to save the created user in the session so the website allows access. Redirect back to the home page.
6. If the user already exists, authenticate the user in the session and redirect to the home page.

Note: In a real world application, you may want to consider using a flag to separate out users registered on your site vs. logging in with social media.

The final thing to do is to add a button on the website to allow users to make use of the new functionality! Open login.leaf and, under </form>, add the following:

<a href="/login-google">
  <img class="mt-3" src="/images/sign-in-with-google.png"
   alt="Sign In With Google">
</a>

The sample project for this chapter contains a new, Google-provided image, sign-in-with-google.png, to display a Sign in with Google button. This adds the image as a link to /login-google — the route provided to Imperial to start the login.

Save the Leaf template and build and run the application in Xcode. Visit http://localhost:8080 in your browser.

Click Create An Acronym and the application takes you to the login page. You’ll see the new Sign in with Google button:

Click the new button and the application takes you to a Google page to allow the TIL application access to your information:

Select the account you want to use and the application redirects you back to the home page. Go to the All Users screen and you’ll see your new user account. If you create an acronym, the application also uses that new user.

Where to go from here?

In this chapter, you learned how to integrate Google login into your website using Imperial and OAuth. This allows users to sign in with their existing Google accounts!

The next chapter shows you how to integrate another popular OAuth provider: GitHub.