diff --git a/src/http-server.ts b/src/http-server.ts
index 46f1fe8..2692c17 100644
--- a/src/http-server.ts
+++ b/src/http-server.ts
@@ -37,7 +37,11 @@ export interface HttpServerInstance {
  * 2. X-OpenProject-Api-Key: <key>
  * 3. ?apiKey=<key> query parameter
  */
-export function extractApiKey(req: Request, url: URL): string | undefined {
+export function extractApiKey(
+  req: Request,
+  url: URL,
+  defaultApiKey?: string
+): string | undefined {
   const authHeader = req.headers.get("authorization");
   if (authHeader) {
     const match = authHeader.match(/^Bearer\s+(.+)$/i);
@@ -56,6 +60,10 @@ export function extractApiKey(req: Request, url: URL): string | undefined {
     return queryKey.trim();
   }
 
+  if (defaultApiKey && defaultApiKey.trim().length > 0) {
+    return defaultApiKey.trim();
+  }
+
   return undefined;
 }
 
@@ -192,7 +200,7 @@ export async function startHttpServer(config: AppConfig): Promise<HttpServerInst
           });
         }
 
-        const apiKey = extractApiKey(req, url);
+        const apiKey = extractApiKey(req, url, config.apiKey);
         if (!apiKey) {
           return new Response(
             JSON.stringify({
diff --git a/tests/http-server.test.ts b/tests/http-server.test.ts
index 64286d4..ffd9fb1 100644
--- a/tests/http-server.test.ts
+++ b/tests/http-server.test.ts
@@ -243,6 +243,27 @@ describe("Hosted Remote MCP Server (HTTP/SSE)", () => {
     expect(res.headers.get("access-control-allow-methods")).toContain("GET");
   });
 
+  test("GET /sse falls back to config.apiKey when configured on server", async () => {
+    const singleTenantServer = await startHttpServer({
+      baseUrl: "https://mock.openproject.example.com",
+      readOnly: true,
+      port: 0,
+      host: "127.0.0.1",
+      apiKey: "server-configured-key",
+    });
+
+    const res = await fetch(`http://127.0.0.1:${singleTenantServer.port}/sse`, {
+      headers: { Accept: "text/event-stream" },
+    });
+    expect(res.status).toBe(200);
+    const reader = res.body?.getReader();
+    const { value } = await reader!.read();
+    const text = new TextDecoder().decode(value);
+    expect(text).toContain("event: endpoint");
+    await reader!.cancel();
+    await singleTenantServer.stop();
+  });
+
   test("concurrent clients with different API keys maintain isolated sessions", async () => {
     // Client A
     const resA = await fetch(`${serverUrl}/sse?apiKey=user-a-secret`, {