[Answer]-LinkedIn Authentication

Your login code is redirecting to the OAuth 2.0 endpoint https://www.linkedin.com/uas/oauth2/authorization but your callback loginsuccess is trying to fetch the OAuth 1.0a token from https://api.linkedin.com/uas/oauth/accessToken. You need to update your access_token_url to the OAuth 2.0 endpoint https://www.linkedin.com/uas/oauth2/accessToken per the LinkedIn docs.