code: def _get_subject(self):
          
          subject_context = SubjectContext(yosai=self, security_manager=self.security_manager)
          subject = self.security_manager.create_subject(subject_context=subject_context)
          global_subject_context.stack.append(subject)
          return subject
docs: Returns the currently accessible Subject available to the calling code
          depending on runtime environment.
  
          :returns: the Subject currently accessible to the calling code