What is AppleAuth?

AppleAuth is a very simple library for Java, based on Google Api Client, that encapsulates logic for communicating with Apple's REST API for Sign in with Apple. The main goal is to make the implementation of Sign in with Apple easier for any web application.

Prerequisites

Configure Sign in with Apple from the Developer Portal

In order to use Sign in with Apple you must enroll in the Apple Developer Program. After you have enrolled in the program go to Developer Account Help and navigate to Configure app capabilities > Sign in with Apple. There you can find the information for configuring Sign in with Apple for your app.

Display the "Sign in with Apple" button

Next, you have to configure your web page for Sign in with Apple. Follow the guidelines from the official documentation. You can also refer to this link to see how to setup the styles of the buttons.

Example

Using AppleAuthProvider.java AppleClientPrivateKeyFactory.java

First order of business should be creating an instance of ECPrivateKey representing the client's(your) private key.
AppleKeyProvider can help you create a ECPrivateKey if you have your private key as string or stream (from a p8 for example).

Creating a new instance of AppleAuthProvider, should be trivial at this point. The only two parameters that are not self explanatory are the SecretGenerator and the collection of scopes.
SecretGenerator is responsible for creating the auth's client_secret. A new instance of the class should cover most of the use cases. scopes is a collection that determines what information will re required from apple and what information will be populated in the returned id_token.

Note: AppleAuthProvider is thread safe and is intended to be long lived. For best performance, we recommend you create a single instance of it, unless you need a second with different parameters.

Once you have your AppleAuthProvider instance you can:

• Call getLoginLink to get an apple oAuth2 login link. You can use the state parameter to carry over information to the redirect url.
• Use makeNewAuthorisationTokenRequest to make a initial authorisation request to apple and retrieve user data based on the auth code from the redirect.
• Use makeNewRefreshTokenRequest to verify that the user is still using 'Sign in with Apple' to sign in your system.

Handling initial response from Apple

After the user clicks on the "Sign in with Apple" button on your page they will be redirected to https://appleid.apple.com/. After they provide their credentials Apple will make a POST request to the url that you have specified as Redirect URL. It will contain a code field. Its contents is what should be handed down to makeNewAuthorisationTokenRequest in order retrieve thee authorization token (it will also contain the state used to create the redirect url). Keep in mind that tokens returned from Apple are short-lived, so you should create a session or a user in your system using the returned AppleAuthorizationToken object. After that you can verify if the user is still logged in using "Sign in with Apple" by retrieving a refresh token using the makeNewRefreshTokenRequest method.

        public class AppleIdTokenManager {
        
            private final static String CLIENT_ID = "Your client id";
            private static final String KEY_ID = "Your Key id";
            private static final String TEAM_ID = "Your team id";
            private static final String REDIRECT_URL = "Your redirect url";
        
            public static void main(String[] args) throws IOException, InvalidKeySpecException {
                //Generating your private key.
                //This could be just a string containing the key.
                InputStream pkStream = AppleIdTokenManager.class
                        .getClassLoader().getResourceAsStream("your_pk_file.p8");
                AppleClientPrivateKeyFactory appleClientPrivateKeyFactory = new AppleClientPrivateKeyFactory();
                ECPrivateKey privateKey = appleClientPrivateKeyFactory.getEcPrivateKey(pkStream);
                
                //Creating provider instance.
                SecretGenerator secretGenerator = new SecretGenerator();
                AppleAuthProvider appleAuthProvider = new AppleAuthProvider(
                        CLIENT_ID,
                        KEY_ID,
                        TEAM_ID,
                        secretGenerator,
                        privateKey,
                        Arrays.asList(AppleUserScope.EMAIL, AppleUserScope.NAME),
                        REDIRECT_URL
                );
                
                //We are ready to start using the provider.

                //Generate a url and navigate the user to it.
                String loginLink = appleAuthProvider.getLoginLink("Some form of state");
                
                //Once the user is redirected back to our domain get the "code" in the request.
                String authCode = "the code in the callback request";
                //Now we can authenticate the user.
                AppleAuthorizationToken initialToken = appleAuthProvider.makeNewAuthorisationTokenRequest(authCode);
                //After the authentication we should check (not more than once every once 24 hours) if the user still 
                // logged in using "Sign in with Apple" by retrieving a refresh token.
                AppleAuthorizationToken refreshToken = appleAuthProvider.makeNewRefreshTokenRequest(initialToken
                        .getRefreshToken());
        
            }
        }