How to sign up new user via Spring Social Facebook?

I am having a website (Angular App) which I can reach on https://localhost:4200 and a server (pure REST API) that is on https://localhost:8443.

Since the REST endpoints are secured, a user must login on my server. Obviously I want users to be able to signup using Facebook and further communicate with my server after login.

According to the docs

POST /signin/{providerId} – Initiates the sign in flow.

that is why there is a button that does just this:

<form ngNoForm name="fb_signin" id="fb_signin" action="https://localhost:8443/signin/facebook" method="POST">
  <input type="hidden" name="scope" value="email">
  <button type="submit">SIGNING</button>
</form>

From there, everything works fine for some time. The user gets redirected to Facebook’s authorization page where the authorization button gets clicked. After that the user gets redirected to https://localhost:8443/signin/facebook.

It seems that per default, in case the user is unknown, there will be a another redirect to https://localhost:8443/signup (see docs)

If the provider user ID matches more than one existing connection, ProviderSignInController will redirect to the application’s sign in URL to offer the user a chance to sign in through another provider or with their username and password. The request to the sign in URL will have an “error” query parameter set to “multiple_users” to indicate the problem so that the page can communicate it to the user. The default sign in URL is “/signin” (relative to the application root), but can be customized by setting the signInUrl property.

On my serer this looks like this (borrowed from a sample application):

@RequestMapping(value = "/signup", method = RequestMethod.GET)
public SignUpForm signupForm(WebRequest request) {
    Connection<?> connection = providerSignInUtils.getConnectionFromSession(request);
    if (connection != null) {
        request.setAttribute("message", new Message(MessageType.INFO, "Your " + StringUtils.capitalize(connection.getKey().getProviderId()) + " account is not associated with a Spring Social Showcase account. If you're new, please sign up."), WebRequest.SCOPE_REQUEST);
        return SignUpForm.fromProviderUser(connection.fetchUserProfile());
    } else {
        return new SignUpForm();
    }
}

And here are my issues:

First of all I need to know what I am supposed to do at this endpoint. The user authorized my app, but my server does not know the user yet so do I

• connection.fetchUserProfile() and save the new user to my database
• something else?

Second, I do not know how I am supposed to redirect back to my website from here which, as explained, lies on https://localhost:4200. But of course, my server does not know that.

Is there a chance somebody can guide me through this?

This is the SocialConfig

@Configuration
@EnableSocial
public class SocialConfig implements SocialConfigurer {

    private final static Logger LOGGER = LogManager.getLogger(SocialConfig.class);

    @Value("${spring.social.facebook.appId}")
    String facebookAppId;

    @Value("${spring.social.facebook.appSecret}")
    String facebookSecret;

    @Autowired
    private DataSource dataSource;

    @Bean
    @Scope(value="singleton", proxyMode = ScopedProxyMode.INTERFACES)
    public ConnectionFactoryLocator connectionFactoryLocator() {
        ConnectionFactoryRegistry registry = new ConnectionFactoryRegistry();

        registry.addConnectionFactory(new FacebookConnectionFactory(
                facebookAppId,
                facebookSecret
        ));

        return registry;
    }

    @Bean
    @Scope(value="singleton", proxyMode=ScopedProxyMode.INTERFACES)
    public UsersConnectionRepository usersConnectionRepository() {
        return new JdbcUsersConnectionRepository(dataSource, connectionFactoryLocator(), Encryptors.noOpText());
    }

    @Override
    public void addConnectionFactories(ConnectionFactoryConfigurer cfConfig, Environment env) {
        LOGGER.debug("Adding connection factories");
        cfConfig.addConnectionFactory(new FacebookConnectionFactory(
                env.getProperty("facebook.clientId"),
                env.getProperty("facebook.clientSecret")));

    }

    @Override
    public UserIdSource getUserIdSource() {
        return new AuthenticationNameUserIdSource();
    }

    @Override
    public UsersConnectionRepository getUsersConnectionRepository(ConnectionFactoryLocator connectionFactoryLocator) {
        return new JdbcUsersConnectionRepository(dataSource, connectionFactoryLocator, Encryptors.noOpText());
    }

    @Bean
    public ProviderSignInController providerSignInController(
            ConnectionFactoryLocator connectionFactoryLocator,
            UsersConnectionRepository usersConnectionRepository) {
        ProviderSignInController controller = new ProviderSignInController(
                connectionFactoryLocator,
                usersConnectionRepository,
                new SimpleSignInAdapter(new HttpSessionRequestCache()));

        return controller;
    }

    @Bean
    public RequestCache requestCache() {
        return new HttpSessionRequestCache();
    }

    @Bean
    public SignInAdapter signInAdapter() {
        return new SimpleSignInAdapter(new HttpSessionRequestCache());
    }

}

Maven dependencies related to Spring Social:

<dependency>
    <groupId>org.springframework.social</groupId>
    <artifactId>spring-social-facebook</artifactId>
    <version>3.0.0.M1</version>
</dependency>
<dependency>
    <groupId>org.springframework.social</groupId>
    <artifactId>spring-social-security</artifactId>
    <version>2.0.0.M4</version>
</dependency>
<dependency>
    <groupId>org.springframework.social</groupId>
    <artifactId>spring-social-core</artifactId>
    <version>2.0.0.M2</version>
</dependency>
<dependency>
    <groupId>org.springframework.social</groupId>
    <artifactId>spring-social-config</artifactId>
    <version>2.0.0.M2</version>
</dependency>