23. GitHub Authentication

Written by Tim Condon

Note: This update is an early-access release. This chapter has not yet been updated to Vapor 4.

In the previous chapter, you learned how to authenticate users using Google. In this chapter, you’ll see how to build upon this and allow users to log in with their GitHub accounts.

Setting up your application with GitHub

To be able to use GitHub OAuth in your application, you must first register the application with GitHub. In your browser, go to https://github.com/settings/developers. Click Register a new application:

Note: You must have a GitHub account to complete this chapter. If you don’t have one, visit https://github.com/join to create one. This chapter also assumes you added Imperial as a dependency to your project in the previous chapter.

Fill in the form with an appropriate name, e.g. Vapor TIL. Set the Homepage URL to http://localhost:8080 for this application and provide a sensible description. Set the Authorization callback URL to http://localhost:8080/oauth/github. This is the URL that GitHub redirects back to once users have allowed your application access to their data:

Click Register application. After it creates the application, the site takes you back to the application’s information page. That page provides the client ID and client secret that you need:

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

Integrating with Imperial

Now that you’ve registered your application with GitHub, you can start integrating Imperial. Open ImperialController.swift and add the following under processGoogleLogin(request:token:):

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

This defines a method to handle the GitHub login, similar to the initial handler for Google logins. The handler simply redirects the user to the home page. Imperial uses this method as the final callback once it has handled the GitHub redirect.

Next, set up the Imperial routes by adding the following at the bottom of boot(router:):

guard let githubCallbackURL =
  Environment.get("GITHUB_CALLBACK_URL") else {
    fatalError("GitHub callback URL not set")
}
try router.oAuth(
  from: GitHub.self,
  authenticate: "login-github",
  callback: githubCallbackURL,
  completion: processGitHubLogin)

Here’s what this does:

• Get the callback URL from an environment variable — this is the URL you set up when registering the application with GitHub.
• Register Imperial’s GitHub OAuth router with your app’s router.
• Tell Imperial to use the GitHub handler.
• Set up the /login-github request as the route that triggers the OAuth flow. This is the route the application uses to allow users to log in via GitHub.
• Provide the callback URL to Imperial.
• Set the completion handler to processGitHubLogin(request:token:) - the method you created above.

As before, you need to provide Imperial the client ID and client secret that GitHub gave you using environment variables. You must also provide the redirect URL. 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:

• GITHUB_CALLBACK_URL: http://localhost:8080/oauth/github — this is the URL you provided to GitHub.
• GITHUB_CLIENT_ID: The client ID provided by GitHub.
• GITHUB_CLIENT_SECRET: The client secret provided by GitHub.

Note: Be sure you still have environment variables set for GOOGLE_CALLBACK_URL, GOOGLE_CLIENT_ID and GOOGLE_CLIENT_SECRET or your app won’t start.

Integrating with web authentication

As in the previous chapter, it’s important to match the experience for a regular login. Again, you’ll create a new user when a user logs in with GitHub for the first time. You can use GitHub’s API with the user’s OAuth token.

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

struct GitHubUserInfo: Content {
  let name: String
  let login: String
}

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

Next, under GitHubUserInfo, add the following:

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

      // 3
      let githubUserAPIURL = "https://api.github.com/user"
      // 4
      return try request
        .client()
        .get(githubUserAPIURL, headers: headers)
        .map(to: GitHubUserInfo.self) { response in
          // 5
          guard response.http.status == .ok else {
            // 6
            if response.http.status == .unauthorized {
              throw Abort.redirect(to: "/login-github")
            } else {
              throw Abort(.internalServerError)
            }
          }
          // 7
          return try response.content
            .syncDecode(GitHubUserInfo.self)
      }
  }
}

Here’s what this does:

1. Add a new function to Imperial’s GitHub service which gets a user’s details from the GitHub 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 GitHub’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 GitHub and return the result.

Next, replace the body of processGitHubLogin(request:token:) with the following:

// 1
return try GitHub
  .getUser(on: request)
  .flatMap(to: ResponseEncodable.self) { userInfo in
    // 2
    return User
      .query(on: request)
      .filter(\.username == userInfo.login)
      .first()
      .flatMap(to: ResponseEncodable.self) { foundUser in
        guard let existingUser = foundUser else {
          // 3
          let user = User(name: userInfo.name,
                          username: userInfo.login,
                          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 GitHub.
2. See if the user exists in the database by looking up the login property as the username.
3. If the user doesn’t exist, create a new User using the name and username from the user information from GitHub. Set the password to a UUID, since you don’t need it.
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.

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-github">
  <img class="mt-3" src="/images/sign-in-with-github.png"
   alt="Sign In With GitHub">
</a>

The sample project for this chapter contains a new image, sign-in-with-github.png, to display a Sign in with GitHub button. This adds the image as a link to /login-github — the route provided to Imperial to start the login. Build and run the application and then 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 GitHub button next to the Sign in with Google button.

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

Click the Authorize button that you see there 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 GitHub login into your website using Imperial and OAuth. This complements the Google and first-party sign in experiences. This allows your users to choose a range of options for authentication.

In the next chapter, you’ll learn how to integrate with a third party email provider. You’ll use another community package and learn how to send emails. To demonstrate this, you’ll implement a password reset flow into your application in case users forget their password.