* return 403 instead of 404 in the following sitations:
* viewing an RSS feed without necessary auth
* accessing a file with the wrong filekey
* accessing a file/folder without necessary auth
(would previously 404 for intentional ambiguity)
* only allow PROPFIND if user has either read or write;
previously a blank response was returned if user has
get-access, but this could confuse webdav clients into
skipping authentication (for example AuthPass)
* return 401 basic-challenge instead of 403 if the client
appears to be non-graphical, because many webdav clients
do not provide the credentials until they're challenged.
There is a heavy bias towards assuming the client is a
browser, because browsers must NEVER EVER get a 401
(tricky state that is near-impossible to deal with)
* return 401 basic-challenge instead of 403 if a PUT
is attempted without any credentials included; this
should be safe, as graphical browsers never do that
this fixes the interoperability issues mentioned in
https://github.com/authpass/authpass/issues/379
where AuthPass would GET files without providing the
password because it expected a 401 instead of a 403;
AuthPass is behaving correctly, this is not a bug
2ce8233921