fix(proxy): keep alias rewrite off pass-through bodies and auth-merged params

Skip router_settings.model_group_alias resolution on registered pass-through
routes, rebuild the rewritten body from the cached client payload instead of the
auth-enriched request_data, and centralize the resolved-scope sentinel in
litellm/constants.py

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm/constants.py

@@ -318,6 +318,7 @@ BEDROCK_REALTIME_PENDING_SESSION_UPDATE_SCOPE_KEY: Final = "litellm.bedrock_real
 BEDROCK_REALTIME_SESSION_COMMITTED_SCOPE_KEY: Final = "litellm.bedrock_realtime.session_committed"
 BEDROCK_REALTIME_COMMITTED_FAILURE_SCOPE_KEY: Final = "litellm.bedrock_realtime.committed_failure"
 CLIENT_REQUESTED_MODEL_SCOPE_KEY: Final = "litellm.client_requested_model"
+MODEL_GROUP_ALIAS_RESOLVED_SCOPE_KEY: Final = "litellm.model_group_alias_resolved"
 REALTIME_SESSION_SUCCESS_LOGGED_KEY: Final = "realtime_session_success_logged"
 REALTIME_SESSION_FAILURE_LOGGED_KEY: Final = "realtime_session_failure_logged"
 

litellm/proxy/auth/user_api_key_auth.py

@@ -32,6 +32,7 @@ from litellm.constants import (
     INVALID_VIRTUAL_KEY_ERROR_MESSAGE,
     LITELLM_PROXY_BUDGET_NAME,
     LITELLM_PROXY_MASTER_KEY_ALIAS,
+    MODEL_GROUP_ALIAS_RESOLVED_SCOPE_KEY,
 )
 from litellm.integrations.otel.model.config import is_otel_v2_enabled
 from litellm.integrations.otel.runtime import phase_span, seed_request_identity
@@ -104,6 +105,7 @@ from litellm.proxy.common_utils.http_parsing_utils import (
     _safe_set_request_parsed_body,
     populate_request_with_path_params,
     read_raw_json_body,
+    rewrite_request_model,
 )
 from litellm.proxy.common_utils.model_listing_utils import claude_code_requested_group
 from litellm.proxy.common_utils.realtime_utils import _realtime_request_body
@@ -237,22 +239,7 @@ async def _normalize_claude_model(
         request.scope[_CLAUDE_MODEL_NORMALIZED] = True
     if source is None:
         return
-    _rewrite_request_model(request_data, request, source)
-
-
-def _rewrite_request_model(
-    request_data: dict,  # mutable-ok: the request body is rewritten in place for every downstream reader
-    request: Request | None,
-    model: str,
-) -> None:
-    request_data["model"] = model
-    _safe_set_request_parsed_body(request=request, parsed_body=request_data)
-    if request is not None:
-        request._json = request_data
-        request._body = orjson.dumps(request_data)
-
-
-_MODEL_GROUP_ALIAS_RESOLVED: Final = "litellm.model_group_alias_resolved"
+    rewrite_request_model(request_data, request, source)
 
 
 async def _resolve_router_settings_model_group_alias(
@@ -264,13 +251,16 @@ async def _resolve_router_settings_model_group_alias(
     """Rewrite the requested model through the key's or team's ``router_settings.model_group_alias``
     before the allowlist checks, so they authorize the model group the request is routed to.
     """
+    from litellm.proxy.pass_through_endpoints.pass_through_endpoints import InitPassThroughEndpointHelpers
     from litellm.proxy.proxy_server import llm_router, prisma_client, proxy_config, proxy_logging_obj
 
     if request is None or llm_router is None or not RouteChecks.is_llm_api_route(route=route):
         return
-    if request.scope.get(_MODEL_GROUP_ALIAS_RESOLVED) is True:
+    if request.scope.get(MODEL_GROUP_ALIAS_RESOLVED_SCOPE_KEY) is True:
+        return
+    request.scope[MODEL_GROUP_ALIAS_RESOLVED_SCOPE_KEY] = True
+    if InitPassThroughEndpointHelpers.is_registered_pass_through_route(route=route):
         return
-    request.scope[_MODEL_GROUP_ALIAS_RESOLVED] = True
     requested: Final = request_data.get("model")
     if not isinstance(requested, str) or await read_raw_json_body(request=request) is None:
         return
@@ -284,7 +274,7 @@ async def _resolve_router_settings_model_group_alias(
         return
     verbose_proxy_logger.debug("router_settings.model_group_alias resolved %s -> %s before auth", requested, target)
     request.scope.setdefault(CLIENT_REQUESTED_MODEL_SCOPE_KEY, requested)
-    _rewrite_request_model(request_data, request, target)
+    rewrite_request_model(request_data, request, target)
 
 
 def _get_model_names_for_budget_checks(

litellm/proxy/common_utils/http_parsing_utils.py

@@ -266,6 +266,24 @@ def _safe_set_request_parsed_body(
         verbose_proxy_logger.debug("Unexpected error setting request parsed body - %s", e)
 
 
+def rewrite_request_model(
+    request_data: dict,  # mutable-ok: the request body is rewritten in place for every downstream reader
+    request: Request | None,
+    model: str,
+) -> None:
+    """Point the auth-time payload, the parsed-body cache, ``request.json()`` and ``request.body()`` at ``model``.
+    The cache and raw body keep only the keys the client sent, not params auth merged into ``request_data``.
+    """
+    request_data["model"] = model
+    if request is None:
+        return
+    cached_body: Final = _safe_get_request_parsed_body(request=request)
+    body: Final = {**cached_body, "model": model} if cached_body is not None else request_data
+    _safe_set_request_parsed_body(request=request, parsed_body=body)
+    request._json = body
+    request._body = orjson.dumps(body)
+
+
 def _safe_get_request_headers(request: Request | None) -> dict:
     """
     [Non-Blocking] Safely get the request headers.

tests/test_litellm/proxy/auth/test_user_api_key_auth.py

@@ -8209,6 +8209,44 @@ async def test_router_settings_model_group_alias_leaves_form_bodies_alone(monkey
     assert get_client_requested_model(request) is None
 
 
+@pytest.mark.asyncio
+async def test_router_settings_model_group_alias_rewrite_keeps_query_params_out_of_body(monkeypatch):
+    """LIT-3054: auth merges query params into its own copy of the body; the rewrite must not forward them."""
+    from litellm.proxy.auth.user_api_key_auth import _enforce_key_and_fallback_model_access
+    from litellm.proxy.common_utils.http_parsing_utils import _read_request_body, populate_request_with_path_params
+
+    router = _alias_router()
+    monkeypatch.setattr(litellm.proxy.proxy_server, "llm_router", router)
+    body = {"model": "AgentX-LLM", "messages": [{"role": "user", "content": "hi"}]}
+    request = _alias_request("/v1/chat/completions", body)
+    request.scope["query_string"] = b"api-version=2024-10-21&stream=true"
+    data = populate_request_with_path_params(request_data=await _read_request_body(request), request=request)
+    assert data["api-version"] == "2024-10-21"
+    token = _alias_token(monkeypatch, "key", {"AgentX-LLM": "claude-haiku"}, ["claude-haiku"])
+    await _enforce_key_and_fallback_model_access(valid_token=token, request_data=data, route="/v1/chat/completions", request=request, llm_model_list=router.model_list, llm_router=router)
+    downstream = await _read_request_body(request)
+    assert downstream == {**body, "model": "claude-haiku"}
+    assert json.loads(await request.body()) == downstream
+    assert await request.json() == downstream
+
+
+@pytest.mark.asyncio
+async def test_router_settings_model_group_alias_leaves_pass_through_bodies_alone(monkeypatch):
+    """LIT-3054: pass-through routes forward the body verbatim to the provider, so auth must not rewrite it."""
+    from litellm.proxy.auth.user_api_key_auth import _enforce_key_and_fallback_model_access
+
+    router = _alias_router()
+    monkeypatch.setattr(litellm.proxy.proxy_server, "llm_router", router)
+    data = {"model": "AgentX-LLM", "messages": [{"role": "user", "content": "hi"}]}
+    route = "/anthropic/v1/messages"
+    request = _alias_request(route, data)
+    token = _alias_token(monkeypatch, "key", {"AgentX-LLM": "claude-haiku"}, ["claude-haiku", "AgentX-LLM"])
+    await _enforce_key_and_fallback_model_access(valid_token=token, request_data=data, route=route, request=request, llm_model_list=router.model_list, llm_router=router)
+    assert data["model"] == "AgentX-LLM"
+    assert (await request.json())["model"] == "AgentX-LLM"
+    assert get_client_requested_model(request) is None
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize("target, expect_denied", [("claude-haiku", False), ("claude-sonnet", True)])
 async def test_router_settings_model_group_alias_authorizes_target_for_team(monkeypatch, target, expect_denied):