We have custom legacy backend written in perl language with REST API exposed via Perl framework. On frontend (SPA application) we are using older AngularJS not Angular. We want to add additional authentication methods or buttons such as Facebook, Linkedin, Google, etc. to our core custom authentication. What is best way to do this? We need backend to verify the token of some sort so we can make sure they are fully authenticed via external method like Facebook, and we also need to extract information about the user so we can sync the email and name into our local database.
Please let us know.