fix: use the pooled client timeout for the Anthropic Messages passthrough (#27675)

* fix: use the pooled client timeout for the Anthropic Messages passthrough

The native `/api/v1/messages` passthrough still referenced `openai.AIOHTTP_CLIENT_TIMEOUT`, which stopped existing when `routers/openai.py` moved onto `session_pool.get_client_timeout()`. Every passthrough request therefore raised `AttributeError: module 'open_webui.routers.openai' has no attribute 'AIOHTTP_CLIENT_TIMEOUT'` before it was sent, and the surrounding handler turned that into a 502 "Open WebUI: Server Connection Error", so Anthropic-format clients such as Cline could not reach any model at all.

Use `get_client_timeout(stream=...)` like the OpenAI and Ollama proxies do, so the configured `AIOHTTP_CLIENT_TIMEOUT` applies and streaming requests additionally get the idle-read timeout.

Fixes #27595

* fix: authenticate native Anthropic requests with x-api-key

The Anthropic Messages passthrough and the token-count forwarding both build their upstream request through `get_anthropic_request_target`, which sends the connection key as `Authorization: Bearer <key>`. Anthropic's OpenAI-compatible `/chat/completions` endpoint accepts that, which is why the model works in the chat UI, but the native `/v1/messages` and `/v1/messages/count_tokens` endpoints do not: they require the key in `x-api-key` and reject a bearer token with 401 `Invalid bearer token` (and `jwt auth is not yet supported on count_tokens`). They also require an `anthropic-version` header, which was never sent.

For `api.anthropic.com` connections, send `anthropic-version` and move the key into `x-api-key`, dropping the bearer header. Connections using session, OAuth or Entra ID auth keep their token untouched, LiteLLM passthrough connections are unaffected, and admin-configured custom headers still win over both defaults.

Fixes #27695

backend/open_webui/main.py

@@ -267,7 +267,7 @@ from open_webui.utils.oauth import (
 from open_webui.utils.plugin import install_tool_and_function_dependencies
 from open_webui.utils.redis import get_redis_client
 from open_webui.utils.security_headers import SecurityHeadersMiddleware
-from open_webui.utils.session_pool import cleanup_response, get_session, stream_wrapper
+from open_webui.utils.session_pool import cleanup_response, get_client_timeout, get_session, stream_wrapper
 from open_webui.utils.tool_approval import (
     ResolveToolCallForm,
     build_tool_approval_resume_payload,
@@ -1908,7 +1908,7 @@ async def count_message_tokens(
 
 
 async def passthrough_anthropic_messages(request: Request, form_data: dict, user) -> Response | dict:
-    requested_model, payload, url, key, headers, cookies = await openai.get_anthropic_token_count_target(
+    requested_model, payload, url, key, headers, cookies = await openai.get_anthropic_request_target(
         request, form_data, user
     )
     request_url = f'{url.rstrip("/")}/messages'
@@ -1924,7 +1924,7 @@ async def passthrough_anthropic_messages(request: Request, form_data: dict, user
             headers=headers,
             cookies=cookies,
             ssl=AIOHTTP_CLIENT_SESSION_SSL,
-            timeout=aiohttp.ClientTimeout(total=openai.AIOHTTP_CLIENT_TIMEOUT),
+            timeout=get_client_timeout(stream=bool(payload.get('stream'))),
         )
 
         if 'text/event-stream' in response.headers.get('Content-Type', ''):