[feat] plugin: optional API key for the AI summary LLM server

Servers that require authentication (e.g. vLLM or llama.cpp started with
--api-key, or an LLM server behind an authenticating reverse proxy) can
now be configured with an ai_summary.api_key, sent as "Authorization:
Bearer".

The key is administrator configuration only: there is no preference for
it, and it is only sent to the configured base_url.  Users can point the
ai_summary_server preference at a server of their own, and such a server
must not be handed the instance API key -- otherwise every user of the
instance could capture it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

searx/plugins/ai_summary.py

@@ -34,6 +34,12 @@ The requests to the LLM server are sent directly (not via
 :py:obj:`searx.network`), an outgoing proxy configuration is deliberately not
 applied to reach an LLM server in the local network.
 
+A server that requires authentication (e.g. vLLM or llama.cpp started with
+``--api-key``, or an LLM server behind an authenticating reverse proxy) is
+configured with an ``api_key``.  The key is administrator configuration only:
+it is never exposed in the preferences and it is only sent to the server in
+``base_url``, never to a server a user configured (:py:obj:`_server_api_key`).
+
 Configuration of the defaults (:py:obj:`searx.ai_summary.SettingsAISummary`):
 
 .. code:: yaml
@@ -83,8 +89,10 @@ VALID_ROLES = ("user", "assistant")
 MODEL_NAME_REGEXP = re.compile(r"[A-Za-z0-9._:/-]{1,128}")
 
 
-def _get_client(base_url: str, cfg: SettingsAISummary) -> httpx.Client:
-    """HTTP client for one request to the LLM server at ``base_url``."""
+def _get_client(base_url: str, cfg: SettingsAISummary, api_key: str = "") -> httpx.Client:
+    """HTTP client for one request to the LLM server at ``base_url``.  The
+    ``api_key`` (if any) is sent in an ``Authorization: Bearer`` header, see
+    :py:obj:`_server_api_key`."""
     # the OpenAI API paths are prefixed with /v1, unless the base URL already
     # points into an API prefix
     base_url = base_url.rstrip("/")
@@ -92,6 +100,7 @@ def _get_client(base_url: str, cfg: SettingsAISummary) -> httpx.Client:
         base_url += "/v1"
     return httpx.Client(
         base_url=base_url,
+        headers={"Authorization": f"Bearer {api_key}"} if api_key else None,
         timeout=httpx.Timeout(connect=cfg.connect_timeout, read=cfg.read_timeout, write=10.0, pool=10.0),
     )
 
@@ -104,6 +113,42 @@ def _valid_server(url: str) -> bool:
     return parsed.scheme in ("http", "https") and bool(parsed.netloc) and len(url) <= 256
 
 
+def _server_id(url: str) -> tuple[str, str, int, str] | None:
+    """Identity of an LLM server URL (scheme, host, port, path) for comparing
+    two URLs, or ``None`` if the URL is unusable.  The ``/v1`` API prefix is
+    not part of the identity, :py:obj:`_get_client` appends it when missing."""
+    try:
+        parsed = urlparse(url)
+    except ValueError:
+        return None
+    # .hostname (not .netloc) drops the userinfo, so that a server URL like
+    # http://llm.example.org@untrusted.example.org/ is identified by the host
+    # the request is actually sent to (untrusted.example.org)
+    if parsed.scheme not in ("http", "https") or not parsed.hostname:
+        return None
+    port = parsed.port or (443 if parsed.scheme == "https" else 80)
+    path = parsed.path.rstrip("/")
+    if path.endswith("/v1"):
+        path = path[: -len("/v1")].rstrip("/")
+    return (parsed.scheme, parsed.hostname.lower(), port, path)
+
+
+def _server_api_key(cfg: SettingsAISummary, server: str) -> str:
+    """The API key to send to ``server``: the administrator's
+    :py:obj:`cfg.api_key <searx.ai_summary.SettingsAISummary.api_key>` if
+    ``server`` *is* the administrator's server, an empty string otherwise.
+
+    Users can point the ``ai_summary_server`` preference at a server of their
+    own; without this check such a server would be sent the instance's API
+    key, which would hand every user of the instance a way to capture it."""
+    if not cfg.api_key:
+        return ""
+    server_id = _server_id(server)
+    if server_id is None or server_id != _server_id(cfg.base_url):
+        return ""
+    return cfg.api_key
+
+
 def _user_server(request: "SXNG_Request", cfg: SettingsAISummary) -> str:
     """The LLM server URL for this request: the user's ``ai_summary_server``
     preference, or the administrator's default."""
@@ -146,7 +191,7 @@ class SXNGPlugin(Plugin):
         /v1/models``).  The server might not be up when SearXNG starts, a
         failing probe only leaves the model suggestion list empty."""
         try:
-            with _get_client(cfg.base_url, cfg) as client:
+            with _get_client(cfg.base_url, cfg, cfg.api_key) as client:
                 resp = client.get("/models")
                 resp.raise_for_status()
                 models = [model["id"] for model in resp.json().get("data", [])]
@@ -255,7 +300,7 @@ def ai_summary_view() -> flask.Response:
 
     # open the upstream connection before streaming, a connection error is
     # reported as HTTP 502 instead of a line in an already started stream
-    client = _get_client(server, cfg)
+    client = _get_client(server, cfg, _server_api_key(cfg, server))
     stream_ctx = client.stream("POST", "/chat/completions", json=chat_payload)
     upstream = None
     try: