Allow GoogleOAuth2UserDetailsLoader subclasses access to members

Subclasses require access to members so that they can be used when overriding methods. See for example VGML, which overrides createUser:
https://github.com/bencaradocdavies/vgml/blob/master/src/main/java/org/auscope/portal/server/web/security/EmailGoogleOAuth2UserDetailsLoader.java