code: def get_safe_redirect_target(arg='next'):
      
      for target in request.args.get(arg), request.referrer:
          if target:
              redirect_uri = urisplit(target)
              allowed_hosts = current_app.config.get('APP_ALLOWED_HOSTS', [])
              if redirect_uri.host in allowed_hosts:
                  return target
              elif redirect_uri.path:
                  return uricompose(
                      path=redirect_uri.path,
                      query=redirect_uri.query,
                      fragment=redirect_uri.fragment
                  )
      return None
docs: Get URL to redirect to and ensure that it is local.
  
      :param arg: URL argument.
      :returns: The redirect target or ``None``.