server: avoid forwarding auth headers in CORS proxy (#24373)

* server: avoid forwarding auth headers in CORS proxy

* format

* fix test

* fix e2e test

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

tools/ui/src/lib/constants/mcp.ts

@@ -51,6 +51,9 @@ export const EXPECTED_THEMED_ICON_PAIR_COUNT = 2;
 /** CORS proxy URL query parameter name */
 export const CORS_PROXY_URL_PARAM = 'url';
 
+/** Header prefix for headers that should be forwarded by the CORS proxy */
+export const CORS_PROXY_HEADER_PREFIX = 'x-llama-server-proxy-header-';
+
 /** Number of trailing characters to keep visible when partially redacting mcp-session-id */
 export const MCP_SESSION_ID_VISIBLE_CHARS = 5;
 

tools/ui/src/lib/services/mcp.service.ts

@@ -16,6 +16,7 @@ import {
 	DEFAULT_MCP_CONFIG,
 	DEFAULT_CLIENT_VERSION,
 	DEFAULT_IMAGE_MIME_TYPE,
+	CORS_PROXY_HEADER_PREFIX,
 	MCP_PARTIAL_REDACT_HEADERS,
 	CORS_PROXY_ENDPOINT
 } from '$lib/constants';
@@ -133,6 +134,20 @@ export class MCPService {
 		return details;
 	}
 
+	private static addRequestHeaders(
+		requestHeaders: Headers,
+		headers: HeadersInit,
+		useProxy: boolean
+	) {
+		for (const [key, value] of new Headers(headers).entries()) {
+			const proxiedKey =
+				useProxy && !key.toLowerCase().startsWith(CORS_PROXY_HEADER_PREFIX)
+					? `${CORS_PROXY_HEADER_PREFIX}${key}`
+					: key;
+			requestHeaders.set(proxiedKey, value);
+		}
+	}
+
 	private static summarizeError(error: unknown): Record<string, unknown> {
 		if (error instanceof Error) {
 			return {
@@ -271,15 +286,11 @@ export class MCPService {
 				const requestHeaders = new Headers(baseInit.headers);
 
 				if (typeof Request !== 'undefined' && input instanceof Request) {
-					for (const [key, value] of input.headers.entries()) {
-						requestHeaders.set(key, value);
-					}
+					this.addRequestHeaders(requestHeaders, input.headers, useProxy);
 				}
 
 				if (init?.headers) {
-					for (const [key, value] of new Headers(init.headers).entries()) {
-						requestHeaders.set(key, value);
-					}
+					this.addRequestHeaders(requestHeaders, init.headers, useProxy);
 				}
 
 				const request = this.createDiagnosticRequestDetails(

tools/ui/src/lib/utils/api-headers.ts

@@ -1,5 +1,5 @@
 import { config } from '$lib/stores/settings.svelte';
-import { REDACTED_HEADERS } from '$lib/constants';
+import { CORS_PROXY_HEADER_PREFIX, REDACTED_HEADERS } from '$lib/constants';
 import { redactValue } from './redact';
 
 /**
@@ -52,11 +52,20 @@ export function sanitizeHeaders(
 
 	for (const [key, value] of normalized.entries()) {
 		const normalizedKey = key.toLowerCase();
-		const partialChars = partialRedactHeaders?.get(normalizedKey);
+		const unproxiedKey = normalizedKey.startsWith(CORS_PROXY_HEADER_PREFIX)
+			? normalizedKey.slice(CORS_PROXY_HEADER_PREFIX.length)
+			: normalizedKey;
+		const partialChars =
+			partialRedactHeaders?.get(normalizedKey) ?? partialRedactHeaders?.get(unproxiedKey);
 
 		if (partialChars !== undefined) {
 			sanitized[key] = redactValue(value, partialChars);
-		} else if (REDACTED_HEADERS.has(normalizedKey) || redactedHeaders.has(normalizedKey)) {
+		} else if (
+			REDACTED_HEADERS.has(normalizedKey) ||
+			REDACTED_HEADERS.has(unproxiedKey) ||
+			redactedHeaders.has(normalizedKey) ||
+			redactedHeaders.has(unproxiedKey)
+		) {
 			sanitized[key] = redactValue(value);
 		} else {
 			sanitized[key] = value;

tools/ui/src/lib/utils/cors-proxy.ts

@@ -3,7 +3,11 @@
  */
 
 import { base } from '$app/paths';
-import { CORS_PROXY_ENDPOINT, CORS_PROXY_URL_PARAM } from '$lib/constants';
+import {
+	CORS_PROXY_ENDPOINT,
+	CORS_PROXY_HEADER_PREFIX,
+	CORS_PROXY_URL_PARAM
+} from '$lib/constants';
 
 /**
  * Build a proxied URL that routes through llama-server's CORS proxy.
@@ -28,7 +32,7 @@ export function buildProxiedHeaders(headers: Record<string, string>): Record<str
 	const proxiedHeaders: Record<string, string> = {};
 
 	for (const [key, value] of Object.entries(headers)) {
-		proxiedHeaders[`x-proxy-header-${key}`] = value;
+		proxiedHeaders[`${CORS_PROXY_HEADER_PREFIX}${key}`] = value;
 	}
 
 	return proxiedHeaders;