This third and final part in my Stateless Spring Security series is about mixing previous post about JWT token based authentication with spring-social-security. This post directly builds upon it and focusses mostly on the changed parts. The idea is to substitude the username/password based login with "Login with Facebook" functionality based on OAuth 2, but still use the same token based authentication after that.
The user clicks on the "Login with Facebook" button which is a simple link to "/auth/facebook", the SocialAuthenticationFilter notices the lack of additional query parameters and triggers a redirect leading the user of your site to Facebook. They login with their username/password and are redirected back, again to "/auth/facebook" but this time with "?code=...&state=..." parameters specified. (If the user previously logged in at facebook and had a cookie set, facebook will even instantly redirect back and no facebook screen is shown at all to the user.) The fun part is that you can follow this in a browsers network log as it's all done using plain HTTP 302 redirects. (The "Location" header in the HTTP response is used to tell the browser where to go next)