mcp-cors-configuration-when-using-mcp-python-sdk-as-server-and-typescript-a6a77258

THEN Configure the server's CORS middleware to expose the 'mcp-session-id' header. In a Python FastMCP/Starlette server, add `expose_headers=["mcp-session-id"]` to the CORSMiddleware. In an Express.js server, set `exposedHeaders: ['mcp-session-id']` in the CORS configuration.

// Express.js example
app.use(cors({
  exposedHeaders: ['mcp-session-id']
}));

# Python FastAPI/Starlette example
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
    expose_headers=["mcp-session-id"]
)