Deprecating AuthenticationMiddleware

[Tim Graham]

Curtis started a PR [0] that replaces the functionality of AuthenticationMiddleware.process_request():

request.user = SimpleLazyObject(lambda: get_user(request))

with this line in AuthConfig.ready():

HttpRequest.user = cached_property(get_user, 'user')

Before finishing the patch, I'd like to get a few more eyeballs on it to make sure there aren't any downsides to this approach. Thanks!

[0] https://github.com/django/django/pull/8568