Before this change the basic, htpasswd and auth proxy authentication
middlewares let every OPTIONS request through without checking
credentials so that browser CORS preflights, which can't carry
credentials, would succeed.
However in serve webdav the OPTIONS request is answered by the WebDAV
handler whose Allow header depends on whether the path is an existing
file, an existing directory or doesn't exist, so an unauthenticated
client could discover the existence and type of any path on the served
remote even with --user/--pass or --htpasswd set.
After this change he authentication middlewares no longer special-case
OPTIONS. Instead the CORS middleware, which runs before authentication
and owns the --allow-origin setting, answers genuine CORS preflights
itself with an empty 200 carrying the CORS headers only when
--allow-origin is set.
All other OPTIONS requests need credentials like any other method, so
clients which probe with OPTIONS before authenticating will get a 401
challenge and must retry with credentials.
Nick Craig-Wood
25707f2dc6