GHSA-h73q-4w9q-82h4

### Summary

The HTTP/3 redirect handler in `src/hackney_h3.erl` forwards the original request headers (`Authorization`, `Cookie`, `Proxy-Authorization`) and, for 307/308 responses, the original request body to the redirect target without checking whether the target host matches the origin. When `follow_redirect` is enabled and a server responds with a cross-origin `Location`, hackney delivers the caller's credentials verbatim to the attacker-controlled host. The main hackney HTTP/1 client has `maybe_strip_auth_on_redirect/2` (the fix for CVE-2018-1000007); the H3 client was added later without it.

### Details

In `src/hackney_h3.erl`, `handle_redirect/11` (line 165) extracts the redirect target from the server-controlled `Location` header via `get_redirect_location/1` and resolves it with `resolve_redirect_url/2`, which accepts any absolute `http://` or `https://` URL. It then calls `do_request_with_redirect/8` passing the original `Headers` list unchanged. For 307/308 responses, `redirect_method/2` preserves the original method and body, so the POST body is also forwarded.

No comparison is made between the original URL's scheme, host, or port and the redirect target. The downstream `connect/3` opens a new QUIC connection to whatever the `Location` header named, and `build_request_headers/4` serializes the unmodified headers into the QPACK-encoded request.

### PoC

1. Issue an HTTP/3 POST to an attacker-controlled origin with `follow_redirect => true` and an `Authorization: Bearer ...` header. 2. The attacker's server responds `307 Location: https://other.host/collect`. 3. hackney opens a new connection to `other.host` and re-sends the original headers and body, including the bearer token and any `Cookie` headers.

### Impact

Credential and request-body disclosure to attacker-controlled origins. Affects hackney 3.1.1 through 4.0.0 when using the HTTP/3 client with `follow_redirect` enabled. Any upstream that is malicious, compromised, or reachable via DNS/MITM can steal session tokens, bearer credentials, and POST bodies. CVSS v4.0: **6.0 (MEDIUM)**.

## Resources

* Introduction commit: https://github.com/benoitc/hackney/commit/e61b7d04b7826847e1efe614106ef4d580c78eab * Patch commit: https://github.com/benoitc/hackney/commit/c58d5b50bade146360b85caf3dc8065807b08246