def clean_username(self, username, request):
    backend_str = request.session[BACKEND_SESSION_KEY]
    backend = load_backend(backend_str)
    try:
      username = backend.clean_username(username)
    except AttributeError:
      pass
    return username
Allows the backend to clean the username, if the backend defines a
dataset/ETHPy150Open cloudera/hue/desktop/core/src/desktop/middleware.py/SpnegoMiddleware.clean_username