Kyle Carberry 94a2e440a8 fix(chatd): extract session token from cookie for relay header (#22649)
## Problem

When a browser connects to the chat stream via WebSocket, it
authenticates using cookies only — the native WebSocket API cannot set
custom headers like `Coder-Session-Token`. The relay between replicas
copies the original request's `Cookie` header but did **not** set the
`Coder-Session-Token` header as a fallback.

This causes a **401 on the worker replica** when `EnableHostPrefix` is
enabled, because the `HTTPCookies.Middleware` strips bare
`coder_session_token` cookies (expecting the `__Host-` prefix). Without
a `Coder-Session-Token` header fallback, `apiKeyMiddleware` finds no
valid credentials.

### Root Cause

The data flow:
1. Browser → subscriber replica: `Cookie:
__Host-coder_session_token=xxx` (browser sends prefixed cookie)
2. Subscriber's `HTTPCookies.Middleware` normalizes: `Cookie:
coder_session_token=xxx` (strips prefix)
3. `relayHeaders()` copies `Cookie: coder_session_token=xxx` to relay
request
4. Worker replica's `HTTPCookies.Middleware` sees bare
`coder_session_token` → **strips it** (expects `__Host-` prefix)
5. `apiKeyMiddleware` → `APITokenFromRequest`: no cookie, no header →
**401**

## Fix

Modified `relayHeaders()` to extract the session token value from the
`Cookie` header and set it as the `Coder-Session-Token` header when no
explicit session token header is already present. The header is never
stripped by middleware, so the worker replica can always authenticate.

## Testing

- **`TestRelayHeaders`**: Unit tests for the updated `relayHeaders()`
function covering all scenarios (cookie-only, header+cookie, no auth,
nil source)
- **`TestExtractSessionTokenFromCookieHeader`**: Unit tests for the
helper function
- **`TestChatStreamRelay/RelayCookieOnlyAuth`**: Integration test with
plain HTTP, cookie-only WebSocket auth
- **`TestChatStreamRelay/RelayCookieOnlyAuthWithHostPrefix`**:
Integration test with `EnableHostPrefix=true`, confirming the 401 is
fixed
- **`cookieOnlySessionTokenProvider`**: Test helper that simulates
browser WebSocket behavior (sets Cookie header only on WebSocket dials,
no custom headers)

## Files Changed

- `enterprise/coderd/chatd/chatd.go` — `relayHeaders()` fix +
`extractSessionTokenFromCookieHeader()` helper
- `enterprise/coderd/chatd/relay_headers_internal_test.go` — unit tests
(new file)
- `enterprise/coderd/chats_test.go` — integration tests + test helper
type
2026-03-05 05:11:07 +00:00
2022-04-04 11:55:06 -05:00

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