I want to create a login screen where user can login using their facebook/google ID. Operator might not have a operator ID in pega. In this case, it should create a operator ID within pega using the data received after authenticating user with facebook/google.
After authentication once you receive the header information you can parse the header information in Pega Authentication activity(Called from Authentication Service) for Authorization/login/Id creation in Pega on the fly.
From Pega end you may creat a Servlet mapping dedicated to this authentication and call the Authentication servivce name from there which internally calls the Authentication activity
You can refer below thread which has good information on this related requirement. it will help you