Add LinkedIn login and registration to WordPress

Create a LinkedIn App

Login with your LinkedIn account at the following page https://www.linkedin.com/developer/apps then click the "Create application" button. Fill all the required fields of the form and as "website url" enter the url of your website. 

Once an app has been created, you'll be readirected to the settings of your app where you'll find Client ID and Client Secret keys.

Make sure that r_basicprofile and r_emailaddress are enabled.

Under the Authorized Redirect URLs setting enter your website url followed by /?wpumsl=linkedin so if your website url is http://example.com you'll need to type http://example.com/?wpumsl=linkedin and then press the "Add" button.

Add credentials in WordPress

Make a copy of the Client ID and Client Secret keys. Now login into your WordPress dashboard and navigate to "Users -> Settings -> General -> Social Login" and locate the settings LinkedIn Client ID and LinkedIn Client Secret and type the keys from your LinkedIn APP.

Now you're ready to accept logins through LinkedIn.