fix(llm-gateway): reject priority header

src/invocation-plane-services/llm-api-gateway/README.md

@@ -52,6 +52,9 @@ Each request is normalized into a function-scoped request context.
   and is forwarded to NVCF gRPC auth when that adapter is configured.
 - `X-Request-ID` is accepted if present, otherwise the gateway generates one.
 - `X-NVCF-Target-Region` is forwarded into the request context.
+- `X-Priority` is reserved for the gateway and derived from the caller's
+  resolved priority; a client-supplied `X-Priority` on the LLM endpoints is
+  rejected with 400.
 
 Configured functions control the downstream `model`, service tier, routing
 method, and per-function rate limits. Prompt rendering and exact prompt

src/invocation-plane-services/llm-api-gateway/api/BUILD.bazel

@@ -28,6 +28,7 @@ go_library(
         "openai_endpoint_handlers.go",
         "openai_remaining_handlers.go",
         "openai_surface.go",
+        "priority_guard.go",
         "provider_error.go",
         "proxy_handler.go",
         "ratelimit.go",
@@ -84,6 +85,7 @@ go_test(
         "middleware_test.go",
         "model_ids_test.go",
         "openai_routes_test.go",
+        "priority_guard_test.go",
         "rate_limit_accounting_test.go",
         "responses_handler_test.go",
         "session_affinity_test.go",

src/invocation-plane-services/llm-api-gateway/api/priority_guard.go

@@ -0,0 +1,44 @@
+/*
+SPDX-FileCopyrightText: Copyright (c) NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+SPDX-License-Identifier: Apache-2.0
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package api
+
+import (
+	"fmt"
+	"net/http"
+
+	echo "github.com/labstack/echo/v4"
+)
+
+const headerPriority = "X-Priority"
+
+// rejectClientSuppliedPriority rejects requests that arrive with a
+// client-supplied X-Priority header.
+// Registered on the LLM route group, not globally. The check fires on header presence
+// rather than value so a present-but-empty X-Priority (which Header.Get cannot
+// distinguish from absent) is rejected too.
+func rejectClientSuppliedPriority(next echo.HandlerFunc) echo.HandlerFunc {
+	return func(ec echo.Context) error {
+		if len(ec.Request().Header.Values(headerPriority)) > 0 {
+			return echo.NewHTTPError(
+				http.StatusBadRequest,
+				fmt.Sprintf("%s is a reserved header and cannot be set by the client", headerPriority),
+			)
+		}
+		return next(ec)
+	}
+}

src/invocation-plane-services/llm-api-gateway/api/priority_guard_test.go

@@ -0,0 +1,179 @@
+/*
+SPDX-FileCopyrightText: Copyright (c) NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+SPDX-License-Identifier: Apache-2.0
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package api
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	echo "github.com/labstack/echo/v4"
+
+	"github.com/NVIDIA/nvcf/src/invocation-plane-services/llm-gateway/config"
+	"github.com/NVIDIA/nvcf/src/invocation-plane-services/llm-gateway/nvcf"
+)
+
+// newPriorityGuardTestServer wires the production route registration so these
+// tests fail if the guard is ever dropped from the LLM route group.
+func newPriorityGuardTestServer(authClient InvocationAuthClient) *echo.Echo {
+	cfg := config.Default()
+	e := echo.New()
+	e.Use(NewContextMiddleware(cfg))
+	e.Use(NewNVCFAuthMiddleware(authClient))
+	RegisterRoutes(e, NewHandlers(cfg, nil, nil))
+	return e
+}
+
+func TestLLMRoutesRejectClientSuppliedPriority(t *testing.T) {
+	t.Parallel()
+
+	paths := []string{"/v1/chat/completions", "/v1/responses", "/v1/embeddings"}
+	values := []struct {
+		name     string
+		priority string
+	}{
+		{name: "explicit value", priority: "0"},
+		{name: "empty value", priority: ""},
+	}
+
+	for _, path := range paths {
+		for _, value := range values {
+			t.Run(path+" "+value.name, func(t *testing.T) {
+				t.Parallel()
+
+				authClient := &stubInvocationAuthClient{
+					authResponse: &nvcf.InvocationAuthResponse{
+						RoutingKey:   "fn-chat",
+						ClientAuthID: "subject-123",
+						AuthContext:  map[string]string{"ncaId": "nca-456"},
+						RateLimitKey: "nca-456",
+					},
+				}
+
+				e := newPriorityGuardTestServer(authClient)
+
+				req := httptest.NewRequest(
+					http.MethodPost,
+					path,
+					strings.NewReader(`{"model":"fn-chat/company-name/model-name","messages":[{"role":"user","content":"hello"}]}`),
+				)
+				req.Header.Set(echo.HeaderContentType, echo.MIMEApplicationJSON)
+				req.Header.Set(echo.HeaderAuthorization, "Bearer sk-live")
+				req.Header.Set(headerPriority, value.priority)
+				rec := httptest.NewRecorder()
+
+				e.ServeHTTP(rec, req)
+
+				if rec.Code != http.StatusBadRequest {
+					t.Fatalf("status = %d, want %d: %s", rec.Code, http.StatusBadRequest, rec.Body.String())
+				}
+				if !strings.Contains(rec.Body.String(), "reserved header") {
+					t.Fatalf("body = %q, want the reserved-header rejection message", rec.Body.String())
+				}
+			})
+		}
+	}
+
+	// The guard is route middleware on the LLM group, so it runs after the
+	// global auth middleware: the reject does not skip authentication.
+	t.Run("auth runs before the reject", func(t *testing.T) {
+		t.Parallel()
+
+		authClient := &stubInvocationAuthClient{
+			authResponse: &nvcf.InvocationAuthResponse{
+				RoutingKey:   "fn-chat",
+				ClientAuthID: "subject-123",
+				AuthContext:  map[string]string{"ncaId": "nca-456"},
+				RateLimitKey: "nca-456",
+			},
+		}
+
+		e := newPriorityGuardTestServer(authClient)
+
+		req := httptest.NewRequest(
+			http.MethodPost,
+			"/v1/chat/completions",
+			strings.NewReader(`{"model":"fn-chat/company-name/model-name","messages":[{"role":"user","content":"hello"}]}`),
+		)
+		req.Header.Set(echo.HeaderContentType, echo.MIMEApplicationJSON)
+		req.Header.Set(echo.HeaderAuthorization, "Bearer sk-live")
+		req.Header.Set(headerPriority, "0")
+		rec := httptest.NewRecorder()
+
+		e.ServeHTTP(rec, req)
+
+		if rec.Code != http.StatusBadRequest {
+			t.Fatalf("status = %d, want %d: %s", rec.Code, http.StatusBadRequest, rec.Body.String())
+		}
+		if !strings.Contains(rec.Body.String(), "reserved header") {
+			t.Fatalf("body = %q, want the reserved-header rejection message", rec.Body.String())
+		}
+		if authClient.authorizeCalls != 1 {
+			t.Fatalf("authorize calls = %d, want 1", authClient.authorizeCalls)
+		}
+	})
+
+	// The guard is scoped to the LLM route group; non-proxied routes such as
+	// the health endpoints accept requests regardless of X-Priority.
+	t.Run("healthz not rejected", func(t *testing.T) {
+		t.Parallel()
+
+		e := newPriorityGuardTestServer(&stubInvocationAuthClient{})
+
+		req := httptest.NewRequest(http.MethodGet, "/healthz", nil)
+		req.Header.Set(headerPriority, "1")
+		rec := httptest.NewRecorder()
+
+		e.ServeHTTP(rec, req)
+
+		if rec.Code != http.StatusOK {
+			t.Fatalf("status = %d, want %d: %s", rec.Code, http.StatusOK, rec.Body.String())
+		}
+	})
+}
+
+// A request without X-Priority must pass the guard untouched and reach the next
+// handler. Positive control: without this, a guard that rejected unconditionally
+// would still satisfy every rejection case above while breaking all legitimate
+// LLM traffic. The guard runs after authentication in the wired server, so its
+// only remaining job on a clean request is to forward it, which this asserts
+// directly rather than driving the full provider stack behind the LLM routes.
+func TestRejectClientSuppliedPriorityForwardsRequestWithoutHeader(t *testing.T) {
+	t.Parallel()
+
+	forwarded := false
+	next := func(c echo.Context) error {
+		forwarded = true
+		return c.NoContent(http.StatusNoContent)
+	}
+
+	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)
+	rec := httptest.NewRecorder()
+	c := echo.New().NewContext(req, rec)
+
+	if err := rejectClientSuppliedPriority(next)(c); err != nil {
+		t.Fatalf("guard returned error for a request without X-Priority: %v", err)
+	}
+	if !forwarded {
+		t.Fatal("guard did not forward a request without X-Priority to the next handler")
+	}
+	if rec.Code != http.StatusNoContent {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusNoContent)
+	}
+}

src/invocation-plane-services/llm-api-gateway/api/routes.go

@@ -31,7 +31,7 @@ func RegisterRoutes(e *echo.Echo, handlers *Handlers) {
 		return c.NoContent(http.StatusOK)
 	})
 
-	group := e.Group("")
+	group := e.Group("", rejectClientSuppliedPriority)
 	handlers.AsOpenAIChatHandlers().RegisterRoutes(group)
 	handlers.AsResponsesHandlers().RegisterRoutes(group)
 	// proxy handlers only contain embedding route for now, but could be extended to other routes in the future