`HttpRequest.scheme` is `https` if `settings.SECURE_PROXY_SSL_HEADER` is
appropriately set and falls back to `HttpRequest._get_scheme()` (a hook
for subclasses to implement) otherwise.
`WSGIRequest._get_scheme()` makes use of the `wsgi.url_scheme` WSGI
environ variable to determine the request scheme.
`HttpRequest.is_secure()` simply checks if `HttpRequest.scheme` is
`https`.
This provides a way to check the current scheme in templates, for example.
It also allows us to deal with other schemes.
Thanks nslater for the suggestion.
The documentation promises that host validation is disabled when
DEBUG=True, that all hostnames are accepted. Domains not compliant with
RFC 1034/1035 were however being validated, this validation has now been
removed when DEBUG=True.
Additionally, when DEBUG=False a more detailed SuspiciousOperation
exception message is provided when host validation fails because the
hostname is not RFC 1034/1035 compliant.
SuspiciousOperations have been differentiated into subclasses, and
are now logged to a 'django.security.*' logger. SuspiciousOperations
that reach django.core.handlers.base.BaseHandler will now return a 400
instead of a 500.
Thanks to tiwoc for the report, and Carl Meyer and Donald Stufft
for review.