v0.50.258: Opus follow-up — fix multi-param redirect-encoding bug + CHANGELOG

PR #1419 (login session TTL + redirect-back + connectivity probe) had a
real bug in the server-side ?next= construction:

quote(path, safe='/:@!$&'()*+,;=') keeps ? and & literal, so:

(a) /api/sessions?limit=50&offset=0 round-trips as /api/sessions?limit=50
    — the inner & terminates the outer next= value and offset=0 leaks as
    a top-level outer query the login page ignores.

(b) An attacker-controlled path with embedded &next=https://evil.com
    injects a second top-level next parameter. Browsers parse first-match
    (benign), Python parse_qs parses last-match (the evil URL) — the
    parser-divergence is a footgun even though _safeNextPath() in login.js
    rejects the actual exploit.

Fix: encode the entire path?query blob with safe='/' so ?, &, = all
percent-encode. The outer next then holds exactly one path-with-query
string the browser auto-decodes once.

6 regression tests in test_v050258_opus_followups.py pin round-trip behavior
across simple paths, single-query, multi-param queries, attacker-injection
neutralization, and the SESSION_TTL=30d constant.

Full suite: 3610 passed, 0 failed.

CHANGELOG.md

@@ -2,6 +2,15 @@
 
 ## [Unreleased]
 
+## [v0.50.258] — 2026-05-01
+
+### Fixed
+- **Login stability: 30-day session TTL, redirect-back, connectivity probe** — three independent fixes for users on flaky networks (VPN, Tailscale). (1) `SESSION_TTL` extended from 24 hours to 30 days in `api/auth.py` so users no longer get kicked out daily. (2) When a session expires and the user is redirected to `/login`, the server now passes `?next=<original-path>` so `_safeNextPath()` in `static/login.js` redirects them back after a successful login instead of dumping them on the login screen. (3) Login page now probes `/health` on load (a public endpoint) and distinguishes "session expired / wrong password" from "can't reach server" — when the server is unreachable, shows a clear "Cannot reach server — check your VPN / Tailscale connection." message, disables the form, retries every 3 seconds, and auto-reloads the page once the server becomes reachable again. (`api/auth.py`, `static/login.js`) @bsgdigital — PR #1419
+
+### Changed (Opus pre-release advisor)
+- **Login redirect URL encoding fix — multi-param queries no longer truncated** — the original PR #1419 implementation built the outer `?next=` parameter via `quote(path, safe='/:@!$&\'()*+,;=')` which kept `?` and `&` literal. Two problems: (a) paths with multi-param queries (e.g. `/api/sessions?limit=50&offset=0`) round-tripped as `/api/sessions?limit=50` because the inner `&` terminated the outer `next` value, (b) attacker-controlled paths with embedded `&next=...` injected a second top-level `next` parameter (browsers parse first-match, Python parse_qs parses last-match — parser-divergence footgun even though `_safeNextPath()` rejects the actual exploit). Fix encodes the entire `path?query` blob with `safe='/'` so `?`, `&`, `=` all percent-encode. The outer `next` then holds exactly one path-with-query string. 6 regression tests in `test_v050258_opus_followups.py` pin the round-trip behavior across simple paths, single-query paths, multi-param queries, and attacker-injection neutralization. (`api/auth.py`, `tests/test_v050258_opus_followups.py`)
+
+
 ## [v0.50.257] — 2026-05-01
 
 ### Added

api/auth.py

@@ -230,11 +230,32 @@ def check_auth(handler, parsed) -> bool:
     else:
         handler.send_response(302)
         # Pass the original path as ?next= so login.js redirects back after auth.
+        # SECURITY/CORRECTNESS: the inner `?` and `&` MUST be percent-encoded
+        # when stuffed into the outer `?next=` parameter, otherwise:
+        #   (a) multi-param query strings get truncated at the first inner `&`
+        #       (e.g. `/api/sessions?limit=50&offset=0` would round-trip as
+        #       just `/api/sessions?limit=50` after the browser parses the
+        #       outer URL — `offset=0` becomes a separate top-level query
+        #       parameter that the login page ignores).
+        #   (b) attacker-controlled paths could inject a second `next=`
+        #       parameter; per RFC 3986 the duplicate behaviour is undefined
+        #       and parsers diverge (Python's parse_qs returns last-match,
+        #       URLSearchParams returns first-match), opening a query-pollution
+        #       footgun even though _safeNextPath() rejects most malicious
+        #       shapes downstream.
+        # Encoding the entire `path?query` blob with quote(safe='/') turns
+        # `?` → `%3F` and `&` → `%26`, so the outer parameter holds exactly
+        # one path-with-query string and `searchParams.get('next')` returns
+        # the full original URL (the browser auto-decodes once).
+        # (Opus pre-release advisor finding for v0.50.258.)
         import urllib.parse as _urlparse
-        _next = _urlparse.quote(parsed.path or '/', safe='/:@!$&\'()*+,;=')
+        _path_with_query = parsed.path or '/'
         if parsed.query:
-            _next += '?' + parsed.query
-        handler.send_header('Location', '/login?next=' + _urlparse.quote(_next, safe='/:@!$&\'()*+,;=?'))
+            _path_with_query += '?' + parsed.query
+        # safe='/' keeps path separators readable; everything else (including
+        # `?`, `&`, `=`) gets percent-encoded.
+        _next = _urlparse.quote(_path_with_query, safe='/')
+        handler.send_header('Location', '/login?next=' + _next)
         handler.end_headers()
     return False
 

tests/test_v050258_opus_followups.py

@@ -0,0 +1,135 @@
+"""Regression tests for v0.50.258 Opus pre-release follow-up.
+
+PR #1419 introduced server-side `?next=` redirect after session expiry. The
+initial implementation built the outer `next` parameter via:
+
+    _next = quote(path, safe='/:@!$&\'()*+,;=')
+    if query:
+        _next += '?' + query
+    location = '/login?next=' + quote(_next, safe='/:@!$&\'()*+,;=?')
+
+Two problems with this shape:
+
+1. The inner `?` was kept literal because both `quote()` calls had `?` in
+   their `safe` set. Combined with `&` also being kept literal, paths with
+   multi-param queries (`/api/sessions?limit=50&offset=0`) round-tripped as
+   `/api/sessions?limit=50` — the rest got eaten as a top-level outer query
+   parameter the login page ignored.
+
+2. Attacker-controlled paths with embedded `&next=...` could inject a second
+   top-level `next` parameter. Browsers' URLSearchParams.get() returns the
+   first-match (safe), Python's parse_qs returns last-match (unsafe). The
+   downstream `_safeNextPath()` rejects non-`/` prefixes which closed the
+   actual exploit, but the parser-divergence is a footgun.
+
+Fix: percent-encode the entire `path?query` blob with `safe='/'`, so `?`,
+`&`, `=` all get encoded. The outer `next` then holds exactly one
+path-with-query string that the browser auto-decodes once.
+"""
+
+from __future__ import annotations
+
+import re
+import urllib.parse as _urlparse
+from pathlib import Path
+
+REPO = Path(__file__).resolve().parents[1]
+
+
+# ── 1: source-level pin: redirect uses safe='/' encoding ────────────────────
+
+
+def test_login_redirect_uses_path_only_safe_encoding():
+    """The check_auth redirect must encode `?` and `&` so multi-param query
+    strings round-trip correctly. Negative pattern guards revert to the
+    original `safe='/:@!$&\'()*+,;=?'` shape."""
+    src = (REPO / "api" / "auth.py").read_text(encoding="utf-8")
+
+    redirect_idx = src.find("/login?next=")
+    assert redirect_idx != -1, "login redirect missing"
+    block = src[max(0, redirect_idx - 1200) : redirect_idx + 600]
+
+    # Must use safe='/' (path-separators only).
+    assert "safe='/'" in block, (
+        "check_auth must encode `?` and `&` in the next= parameter so multi-param "
+        "query strings round-trip. safe='/' is the correct encoding shape."
+    )
+
+    # Must NOT use the broad safe set that keeps `?` and `&` literal.
+    assert "safe='/:@!$&\\'()*+,;=?'" not in block, (
+        "check_auth must not use the broad safe='/:@!$&\\'()*+,;=?' encoding — "
+        "that keeps `?` and `&` literal, which truncates multi-param queries "
+        "and creates a parser-divergence footgun."
+    )
+
+
+# ── 2: behavioral round-trip ────────────────────────────────────────────────
+
+
+def _build_redirect_like_check_auth(path: str, query: str) -> str:
+    """Mirror api.auth.check_auth's redirect construction so we can assert
+    the round-trip without spinning up a server."""
+    _path_with_query = path or "/"
+    if query:
+        _path_with_query += "?" + query
+    _next = _urlparse.quote(_path_with_query, safe="/")
+    return "/login?next=" + _next
+
+
+def _browser_searchparams_get_next(location: str) -> str:
+    """Mirror the browser's URLSearchParams.get('next') behaviour."""
+    parsed = _urlparse.urlparse("https://host" + location)
+    qs = _urlparse.parse_qs(parsed.query, keep_blank_values=True)
+    values = qs.get("next", [])
+    return values[0] if values else None
+
+
+def test_redirect_roundtrip_simple_path():
+    location = _build_redirect_like_check_auth("/foo/bar", "")
+    assert _browser_searchparams_get_next(location) == "/foo/bar"
+
+
+def test_redirect_roundtrip_single_query_param():
+    location = _build_redirect_like_check_auth("/foo/bar", "baz=qux")
+    assert _browser_searchparams_get_next(location) == "/foo/bar?baz=qux"
+
+
+def test_redirect_roundtrip_multi_query_params():
+    """REGRESSION: pre-fix, this round-tripped to `/api/sessions?limit=50`
+    (offset got eaten as a top-level outer query)."""
+    location = _build_redirect_like_check_auth("/api/sessions", "limit=50&offset=0")
+    got = _browser_searchparams_get_next(location)
+    assert got == "/api/sessions?limit=50&offset=0", (
+        f"multi-param query round-trip broken: got {got!r}, expected the full string"
+    )
+
+
+def test_redirect_roundtrip_attacker_controlled_next_injection_neutralized():
+    """REGRESSION: pre-fix, an attacker-controlled `&next=https://evil.com`
+    in the source query injected a second top-level `next` parameter.
+    Browsers parse first-match (benign), Python parses last-match (the evil
+    value) — parser-divergence footgun even if downstream guards reject it."""
+    location = _build_redirect_like_check_auth(
+        "/admin", "action=foo&next=https://evil.com"
+    )
+    got = _browser_searchparams_get_next(location)
+    # The entire string is preserved as the FIRST `next` value.
+    assert got == "/admin?action=foo&next=https://evil.com"
+    # And there is exactly ONE top-level `next` parameter.
+    parsed = _urlparse.urlparse("https://host" + location)
+    qs = _urlparse.parse_qs(parsed.query, keep_blank_values=True)
+    assert len(qs.get("next", [])) == 1, (
+        f"expected exactly one top-level `next` parameter, got {qs.get('next')}"
+    )
+    # _safeNextPath() in login.js (charAt(0)==='/' and charAt(1)!=='/') would
+    # accept this as a valid same-origin path. The /admin page receives the
+    # benign embedded query and the evil URL never becomes a redirect target.
+
+
+def test_redirect_session_ttl_30_days():
+    """Pin the SESSION_TTL constant to the 30-day value introduced by #1419."""
+    src = (REPO / "api" / "auth.py").read_text(encoding="utf-8")
+    assert "SESSION_TTL = 86400 * 30" in src, (
+        "SESSION_TTL must be 30 days (86400 * 30) per #1419. Reverting to "
+        "24h would re-introduce the daily-kick-out UX regression."
+    )