SameHost compares two URLs by host name (case insensitively) and port
(treating the scheme's default port as no port) so redirect policies
can tell a real change of host from a server spelling its own host
differently, e.g. redirecting "https://example.com/" to
"https://EXAMPLE.com:443/".
The HTTPS downgrade check now compares the redirect target against
the original request rather than the previous hop, so a chain which
started on plaintext http, passed through an https server and came
back to http is no longer refused - nothing is being downgraded
relative to what the user asked for. A chain which started on https
and reaches http via any number of hops is still refused.
A server that redirects an HTTPS request to a plaintext HTTP URL on the
same host would cause Go's http.Client to replay the configured
credentials (Basic Authorization, cookies, secret headers) over the
network in cleartext.
Refuse to follow such downgrade redirects by default in lib/rest and wire
the webdav backend's client to use it. The `auth_redirect` option remains
the opt-in escape hatch for servers that legitimately need auth preserved
across redirects.
Fixes GHSA-h4mf-4v27-hggj
Nick Craig-Wood