How it works...

This recipe presented you with how you can create an application that interacts with LinkedIn to retrieve the user's profile using OAuth 2.0 protocol. This recipe relies on Spring Social Provider for LinkedIn, which saves us from having to create a controller to deal with OAuth 2.0 callbacks as well as building URLs for authorization and token requests. This recipe differs from other recipes using Spring Social because it presents one provider implementation which support Spring Boot's auto-configuration feature, so we don't need to create any configuration classes.

Besides the fact that a lot of OAuth 2.0's details are abstracted behind Spring Social, all the steps happen when we run the application and start the authorization flow. In fact, as we are using the Authorization Code grant type, the application retrieves the access token through two steps, which are authorization and token request.

To start the authorization flow you must go to http://localhost:8080/ which, in case of being not connected the user's LinkedIn account with the social-linkd application, should be redirected to /connect/linkedin:

The redirection is performed by the method profile from the ProfileController class. As the controller and this method do not define any paths for a request, it will be defined as / by default. As you may notice in the following code, the first thing the method repositories do is to check if the current user has connected her account with the application, which is social-linkedin:

if (connectionRepository.findPrimaryConnection(LinkedIn.class) == null) { 
    return "redirect:/connect/linkedin"; 
} 

The endpoint /connect/linkedin maps directly to the method connectionStatus from the ConnectController class of Spring Social. If there is no connection, this method calls the private method connectView which builds the name {providerId}Connect, which in LinkedIn's case is linkedinConnect. This is exactly the name of the view we created as linkedinConnect.html.

Open the file linkedinConnect.html to see which scope the application is asking for LinkedIn, and you must realize that it is r_basicprofile. All the available scopes defined by LinkedIn should be retrieved by accessing the application dashboard which is present in the section Default Application Permissions.

Back to the page generated by linkedinConnect view, if you click on the Connect to LinkedIn button, you will be redirected to LinkedIn, which will ask you for your credentials and for your consent.

Notice that LinkedIn, unlike many other OAuth 2.0 Providers, asks for permission at the same time it authenticates the user. If you click on Allow Access and send your credentials at the authentication form, social-linkd will receive the authorization code and will use it to retrieve an access token and create the connection for the current user within the application. Then, if there is a connection, the private method connectedView from ConnectController will be called, which will render the following HTML page defined by linkedinConnected.html:

Clicking on the link here, you will then be redirected to the main page, where your profile name will be presented as follows: