To build a secure WebSocket server in Python, you need to implement several features such as CORS, authentication, and rate limiting. The python-socketio library provides many built-in features for implementing these measures, including automatic HTTP compression, cross-origin resource sharing (CORS), user authentication, and payload size restriction. To enable CORS, you can set the cors_allowed_origins parameter when initializing the WebSocket server instance. This allows or blocks domains from making cross-origin requests. Additionally, you should authenticate WebSocket clients before connecting using a username and password system. The server verifies the credentials and checks if they exist in a database before authenticating the user. To prevent denial-of-service (DoS) and distributed denial-of-service (DDoS) attacks, you can enforce rate limiting on your server by limiting the frequency of API requests each user can make. You should also restrict payload size to protect your WebSocket server from crashes caused by oversized messages. Finally, use TLS/SSL encryption to secure socket communication and ensure that sensitive information is not stolen via man-in-the-middle attacks.