Return request.getSession().setAttribute("PRINCIPAL", facebookPrincipal) back. Make method handleAuthenticationResponse public, so applications, which don't need principal in httpSession to call it directly

1) Revert removal of principal from httpSession in request.getSession().setAttribute("PRINCIPAL", facebookPrincipal) . 

2) Make method handleAuthenticationResponse public, so applications, which don't need principal in httpSession, can use it directly